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Donella H. Meadows
Dennis L. Meadows
J^rgen Randers
William W. Behrens III

A Report for THE CLUB OF ROME'S Project on the
Predicament of Mankind

A POTOMAC ASSOCIATES BOOK $ 2.75

THE LIMITS TO GROWTH

Other Potomac Associates Boo\s

HOPES AND FEARS OF THE AMERICAN PEOPLE

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Street NW, Washington, DC 20036.

A POTOMAC ASSOCIATES BOOK

A REPORT FOR

THE CLUB OF ROME'S PROJECT ON
THE PREDICAMENT OF MANKIND

Donella H. Meadows
Dennis L. Meadows
J0rgen Randers
William W. Behrens III

Universe Books

NEW YORK

All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system, or transmitted in any form or by any
means, electronic, mechanical, photocopying, recording, or otherwise,
without the prior permission of Potomac Associates.

Second printing before publication 1972
Third printing 1972
Fourth printing 1972
Fifth printing 1972

Library of Congress Catalog Card Number: 73-187907

ISBN 0-87663-165-0

Design by Hubert Leckie

Printed in the United States of America

Published in the United States of America in 1972 by Universe Books,
381 Park Avenue South, New York, New York 10016
© 1972 by Dennis L. Meadows

To Dr. Aurelio Peccei, whose profound concern for humanity
has inspired us and many others to thinks about the world's
long-term problems

The MIT Project Team

Dr. Dennis L. Meadows, director, United States

dr. alison a. Anderson, United States ( pollution )

dr. jay m. anderson, United States ( pollution )

ilyas bayar, Turkey (agriculture)

william w. behrens hi, United States (resources)

farhad hakimzadeh, Iran ( population )

dr. steffen harbordt, Germany ( socio-political trends )

Judith a. machen, United States (administration)

dr. donella h. meadows, United States (population)

peter milling, Germany (capital)

nirmala s. murthy, India ( population )

roger f. naill, United States ( resources )

j^rgen randers, Norway (pollution)

Stephen shantzis, United States (agriculture)

john a. seeger, United States (administration )

Marilyn williams, United States (documentation)

dr. erich k. o. zahn, Germany (agriculture)

FOREWORD

IN APRIL 1968, a group of thirty individuals from ten
countries — scientists, educators, economists, humanists, indus-
trialists, and national and international civil servants — gathered
in the Accademia dei Lincei in Rome. They met at the insti-
gation of Dr. Aurelio Peccei, an Italian industrial manager,
economist, and man of vision, to discuss a subject of staggering
scope — the present and future predicament of man.

THE CLUB OF ROME

Out of this meeting grew The Club of Rome, an informal
organization that has been aptly described as an "invisible
college." Its purposes are to foster understanding of the varied
but interdependent components — economic, political, natural,
and social— that make up the global system in which we all
live; to bring that new understanding to the attention of
policy-makers and the public worldwide; and in this way to
promote new policy initiatives and action.

The Club of Rome remains an informal international asso-
ciation, with a membership that has now grown to approxi-
mately seventy persons of twenty-five nationalities. None of its
members holds public office, nor does the group seek to express
any single ideological, political, or national point of view. All
are united, however, by their overriding conviction that the
major problems facing mankind are of such complexity and
are so interrelated that traditional institutions and policies arc

FOREWORD

no longer able to cope with them, nor even to come to grips
with their full content.

The members of The Club of Rome have backgrounds as
varied as their nationalities. Dr. Peccei, still the prime moving
force within the group, is affiliated with Fiat and Olivetti and
manages a consulting firm for economic and engineering
development, Italconsult, one of the largest of its kind in
Europe. Other leaders of The Club of Rome include: Hugo
Thiemann, head of the Battelle Institute in Geneva; Alexander
King, scientific director of the Organization for Economic
Cooperation and Development; Saburo Okita, head of the
Japan Economic Research Center in Tokyo; Eduard Pestel
of the Technical University of Hannover, Germany; and
Carroll Wilson of the Massachusetts Institute of Technology.
Although membership in The Club of Rome is limited, and
will not exceed one hundred, it is being expanded to include
representatives of an ever greater variety of cultures, nationali-
ties, and value systems.

THE PROJECT ON THE PREDICAMENT OF MANKIND

A series of early meetings of The Club of Rome culminated
in the decision to initiate a remarkably ambitious undertaking
—the Project on the Predicament of Mankind.

The intent of the project is to examine the complex of
problems troubling men of all nations: poverty in the midst
of plenty; degradation of the environment; loss of faith in
institutions; uncontrolled urban spread; insecurity of employ-
ment; alienation of youth; rejection of traditional values; and
inflation and other monetary and economic disruptions. These
seemingly divergent parts of the "world problematique," as
The Club of Rome calls it, have three characteristics in com-

FOREWORD

mon: they occur to some degree in all societies; they contain
technical, social, economic, and political elements; and, most
important of all, they interact.

It is the predicament of mankind that man can perceive the
problematique, yet, despite his considerable knowledge and
skills, he does not understand the origins, significance, and
interrelationships of its many components and thus is unable
to devise effective responses. This failure occurs in large part
because we continue to examine single items in the problema-
tique without understanding that the whole is more than the
sum of its parts, that change in one element means change in
the others.

Phase One of the Project on the Predicament of Mankind
took definite shape at meetings held in the summer of 1970 in
Bern, Switzerland, and Cambridge, Massachusetts. At a two-
week conference in Cambridge, Professor Jay Forrester of the
Massachusetts Institute of Technology (MIT) presented a
global model that permitted clear identification of many spe-
cific components of the problematique and suggested a tech-
nique for analyzing the behavior and relationships of the most
important of those components. This presentation led to initia-
tion of Phase One at MIT, where the pioneering work of Pro-
fessor Forrester and others in the field of System Dynamics had
created a body of expertise uniquely suited to the research
demands.

The Phase One study was conducted by an international
team, under the direction of Professor Dennis Meadows, with
financial support from the Volkswagen Foundation. The
team examined the five basic factors that determine, and there-
fore, ultimately limit, growth on this planet — population, agri-
cultural production, natural resources, industrial production,

FOREWORD

and pollution. The research has now been completed. This
book is the first account of the findings published for general
readership.

A GLOBAL CHALLENGE

It is with genuine pride and pleasure that Potomac Associates
joins with The Club of Rome and the MIT research team in
the publication of The Limits to Growth.

We, like The Club of Rome, are a young organization, and
we believe the Club's goals are very close to our own. Our
purpose is to bring new ideas, new analyses, and new ap-
proaches to persistent problems — both national and interna-
tional — to the attention of all those who care about and help
determine the quality and direction of our life. We are de-
lighted therefore to be able to make this bold and impressive
work available through our book program.

We hope that The Limits to Growth will command critical
attention and spark debate in all societies. We hope that it will
encourage each reader to think through the consequences of
continuing to equate growth with progress. And we hope
that it will lead thoughtful men and women in all fields of
endeavor to consider the need for concerted action now if we
are to preserve the habitability of this planet for ourselves
and our children.

William Watts, President

POTOMAC ASSOCIATES

CONTENTS

FOREWORD

by Potomac Associates page 9
figures page 14
tables page 16
introduction page 17

I The Nature of Exponential Growth page 25

II The Limits to Exponential Growth page 45

III Growth in the World System page 88

IV Technology and the Limits to Growth page J29

V The State of Global Equilibrium page 156

COMMENTARY

by The Club of Rome Executive Committee page

appendix Related Studies page ig8
notes page 201

FIGURES

figure 1 Human Perspectives page 19

figure 2 World Fertilizer Consumption page 26

figure 3 World Urban Population page 27

figure 4 The Growth of Savings page 28

figure 5 World Population page 33

figure 6 World Industrial Production page 38

figure 7 Economic Growth Rates page 40

figure 8 Protein and Caloric Intake page 47

figure 9 Food Production page 49

figure 10 Arable Land page 50

figure 11 Chromium Reserves page 62

figure 12 Chromium Availability page 64

figure 13 Chromium Availability with Double the Known
Reserves page 65

figure 14 Energy Consumption and GNP Per Capita page 70

figure 15 Carbon Dioxide Concentration in the Atmosphere page 72

figure 16 Waste Heat Generation in the Los Angeles Basin page 74

figure 17 Nuclear Wastes page 75

figure 18 Changes in Chemical Characteristics and Commercial
Fish Production in Lake Ontario page 76

figure 19 Oxygen Content of the Baltic Sea page 78

figure 20 US Mercury Consumption page 79

figure 21 Lead in the Greenland Ice Cap page 80

figure 22 DDT Flows in the Environment page S3

figure 23 Population Growth and Capital Growth
Feedback Loops page 95

figure 24 Feedback Loops of Population, Capital, Agriculture,
and Pollution page 97

figure 25 Feedback Loops of Population, Capital,
Services, and Resources page 100

figure 26 The World Model page 102

figure 27 Nutrition and Life Expectancy page 106

figure 28 Industrial Output Per Capita and Resource
Usage page 108

figure 29 World Steel Consumption and GNP Per Capita page no

figure 30 US Copper and Steel Consumption and GNP

Per Capita page in
figure 31 Birth Rates and GNP Per Capita page 112

figure 32 Families Wanting Four or More Children
and GNP Per Capita page 114

figure 33 Desired Family Size page 11$

figure 34 The Effect of Pollution on Lifetime page 120

figure 35 World Model Standard Run page 124

figure 36 World Model with Natural Resource Reserves

Doubled page 127
figure 37 World Model with "Unlimited" Resources page 132
figure 38 Cost of Pollution Reduction page 134

figure 39 World Model with "Unlimited" Resources and
Pollution Controls page 136

figure 40 World Model with "Unlimited" Resources, Pollution

Controls, and Increased Agricultural Productivity page 138
figure 41 World Model with "Unlimited" Resources, Pollution

Controls, and "Perfect" Birth Control page 139
figure 42 World Model with "Unlimited" Resources, Pollution

Controls, Increased Agricultural Productivity, and

"Perfect" Birth Control page 140

figure 43 Modern Whaling page 152
figure 44 World Model with Stabilized Population page 160
figure 45 World Model with Stabilized Population and
Capital page 162

figure 46 Stabilized World Model I page 165

figure 47 Stabilized World Model II page 168

figure 48 World Model with Stabilizing Policies Introduced in
the Year 2000 page 169

TABLES

table 1 Doubling Time page 50

table 2 Economic and Population Growth Rates page 42

table 3 Extrapolated GNP for the Year 2000 page 43

table 4 Nonrenewable Natural Resources page 56

table 5 DDT in Body Fat page S5

table 6 Cost of Reducing Air Pollution in a US City page 735

INTRODUCTION

/ do not wish to seem overdramatic, but
I can only conclude from the Information
that is available to me as Secretary-
General, that the Members of the United
Nations have perhaps ten years left In
which to subordinate their ancient
quarrels and launch a global partnership
to curb the arms race, to improve the
human environment, to defuse the popu-
lation explosion, and to supply the
required momentum to development
efforts. If such a global partnership Is
not forged within the next decade, then
I very much fear that the problems I
have mentioned will have reached such
staggering proportions that they will be
beyond our capacity to control.

U THANT, 1969

The problems U Thant mentions—
the arms race, environmental deterioration, the population ex-
plosion, and economic stagnation — are often cited as the cen-
tral, long-term problems of modern man. Many people believe
that the future course of human society, perhaps even the sur-
vival of human society, depends on the speed and effectiveness
with which the world responds to these issues. And yet only a
small fraction of the world's population is actively concerned
with understanding these problems or seeking their solutions.

HUMAN PERSPECTIVES

Every person in the world faces a series of pressures and prob-
lems that require his attention and action. These problems

INTRODUCTION

affect him at many different levels. He may spend much of
his time trying to find tomorrow's food for himself and his
family. He may be concerned about personal power or the
power of the nation in which he lives. He may worry about
a world war during his lifetime, or a war next week with a
rival clan in his neighborhood.

These very different levels of human concern can be rep-
resented on a graph like that in figure 1. The graph has two
dimensions, space and time. Every human concern can be
located at some point on the graph, depending on how much
geographical space it includes and how far it extends in time.
Most people's worries are concentrated in the lower left-hand
corner of the graph. Life for these people is difficult, and they
must devote nearly all of their efforts to providing for them-
selves and their families, day by day. Other people think
about and act on problems farther out on the space or time
axes. The pressures they perceive involve not only themselves,
but the community with which they identify. The actions they
take extend not only days, but weeks or years into the future.

A person's time and space perspectives depend on his culture,
his past experience, and the immediacy of the problems con-
fronting him on each level. Most people must have successfully
solved the problems in a smaller area before they move their
concerns to a larger one. In general the larger the space and the
longer the time associated with a problem, the smaller the
number of people who are actually concerned with its solution.

There can be disappointments and dangers in limiting one's
view to an area that is too small. There are many examples of
a person striving with all his might to solve some immediate,
local problem, only to find his efforts defeated by events
occurring in a larger context. A farmer's carefully maintained

INTRODUCTION

Figure 1 HUMAN PERSPECTIVES

•

• •

•

• •

•
m

• • • •

:•••:•.•*

• •

•

• •

• •
• • •

• •
• •

•

• •

• • • •

• • •

• • • a
• • •

• • •

• • • •

• • •
• •

• • •

•
•

• •

• • •

• • • • •
• • • •

• • • • •

• mm*
•

• •

next week next few years. lifetime children's lifetime

TIME

Although the perspectives of the world's people vary in space and in time,
every human concern talis somewhere on the space-time graph. The
majority of the world's people are concerned with matters that atlect only
family or friends over a short period of time. Others look farther ahead in
time or over a larger area — a city or a nation. Only a very few people have
a global perspective that extends far into the future.

fields can be destroyed by an international war. Local officials'
plans can be overturned by a national policy. A country's eco-
nomic development can be thwarted by a lack of world demand
for its products. Indeed there is increasing concern today that
most personal and national objectives may ultimately be frus-
trated by long-term, global trends such as those mentioned by
U Thant.

INTRODUCTION

Are the implications of these global trends actually so threat-
ening that their resolution should take precedence over local,
short-term concerns?

Is it true, as U Thant suggested, that there remains less than
a decade to bring these trends under control ?

If they are not brought under control, what will the con-
sequences be ?

What methods does mankind have for solving global prob-
lems, and what will be the results and the costs of employing
each of them ?

These are the questions that we have been investigating in
the first phase of The Club of Rome's Project on the Predica-
ment of Mankind. Our concerns thus fall in the upper right-
hand corner of the space-time graph.

PROBLEMS AND MODELS

Every person approaches his problems, wherever they occur on
the space-time graph, with the help of models. A model is
simply an ordered set of assumptions about a complex system.
It is an attempt to understand some aspect of the infinitely
varied world by selecting from perceptions and past experience
a set of general observations applicable to the problem at hand.
A farmer uses a mental model of his land, his assets, market
prospects, and past weather conditions to decide which crops to
plant each year. A surveyor constructs a physical model — a
map — to help in planning a road. An economist uses mathe-
matical models to understand and predict the flow of inter-
national trade.

Decision-makers at every level unconsciously use mental
models to choose among policies that will shape our future
world. These mental models are, of necessity, very simple when

INTRODUCTION

compared with the reality from which they are abstracted.
The human brain, remarkable as it is, can only keep track of
a limited number of the complicated, simultaneous interactions
that determine the nature of the real world.

We, too, have used a model. Ours is a formal, written model
of the world.* It constitutes a preliminary attempt to improve
our mental models of long-term, global problems by com-
bining the large amount of information that is already in
human minds and in written records with the new informa-
tion-processing tools that mankind's increasing knowledge has
produced — the scientific method, systems analysis, and the
modern computer.

Our world model was built specifically to investigate five
major trends of global concern — accelerating industrialization,
rapid population growth, widespread malnutrition, depletion
of nonrenewable resources, and a deteriorating environment.
These trends are all interconnected in many ways, and their
development is measured in decades or centuries, rather than
in months or years. With the model we are seeking to under-
stand the causes of these trends, their interrelationships, and
their implications as much as one hundred years in the future.

The model we have constructed is, like every other model,
imperfect, oversimplified, and unfinished. We are well aware
of its shortcomings, but we believe that it is the most useful
model now available for dealing with problems far out on the
space-time graph. To our knowledge it is the only formal
model in existence that is truly global in scope, that has a

• The prototype model on which we have based our work was designed
by Professor Jay W. Forrester of the Massachusetts Institute of Tech-
nology. A description of that model has been published in his book
World Dynamics (Cambridge, Mass.: Wright-Allen Press, 1971).

INTRODUCTION

time horizon longer than thirty years, and that includes im-
portant variables such as population, food production, and pol-
lution, not as independent entities, but as dynamically inter-
acting elements, as they are in the real world.

Since ours is a formal, or mathematical, model it also has
two important advantages over mental models. First, every
assumption we make is written in a precise form so that it is
open to inspection and criticism by all. Second, after the as-
sumptions have been scrutinized, discussed, and revised to
agree with our best current knowledge, their implications for
the future behavior of the world system can be traced without
error by a computer, no matter how complicated they become.

We feel that the advantages listed above make this model
unique among all mathematical and mental world models
available to us today. But there is no reason to be satisfied with
it in its present form. We intend to alter, expand, and improve
it as our own knowledge and the world data base gradually
improve.

In spite of the preliminary state of our work, we believe it
is important to publish the model and our findings now. De-
cisions are being made every day, in every part of the world,
that will affect the physical, economic, and social conditions
of the world system for decades to come. These decisions can-
not wait for perfect models and total understanding. They will
be made on the basis of some model, mental or written, in any
case. We feel that the model described here is already suffi-
ciently developed to be of some use to decision-makers. Fur-
thermore, the basic behavior modes we have already observed
in this model appear to be so fundamental and general that
we do not expect our broad conclusions to be substantially
altered by further revisions.

INTRODUCTION

It is not the purpose of this book to give a complete, scien-
tific description of all the data and mathematical equations
included in the world model. Such a description can be found
in the final technical report of our project Rather, in The
Limits to Growth we summarize the main features of the
model and our findings in a brief, nontechnical way. The em-
phasis is meant to be not on the equations or the intricacies of
the model, but on what it tells us about the world. We have
used a computer as a tool to aid our own understanding of the
causes and consequences of the accelerating trends that char-
acterize the modern world, but familiarity with computers is
by no means necessary to comprehend or to discuss our con-
clusions. The implications of those accelerating trends raise
issues that go far beyond the proper domain of a purely scien-
tific document. They must be debated by a wider community
than that of scientists alone. Our purpose here is to open that
debate.

The following conclusions have emerged from our work so
far. We are by no means the first group to have stated them.
For the past several decades, people who have looked at the
world with a global, long-term perspective have reached sim-
ilar conclusions. Nevertheless, the vast majority of policy-
makers seems to be actively pursuing goals that are inconsistent
with these results.

Our conclusions are:
1. If the present growth trends in world population, industrial-
ization, pollution, focd production, and resource depletion con-
tinue unchanged, the limits to growth on this planet will be
reached sometime within the next one hundred years. The
most probable result will be a rather sudden and uncontrol-
lable decline in both population and industrial capacity.

INTRODUCTION

2. It is possible to alter these growth trends and to establish a
condition of ecological and economic stability that is sustain-
able far into the future. The state of global equilibrium could
be designed so that the basic material needs of each person on
earth are satisfied and each person has an equal opportunity
to realize his individual human potential.

3. If the world's people decide to strive for this second out-
come rather than the first, the sooner they begin working to
attain it, the greater will be their chances of success.

These conclusions are so far-reaching and raise so many
questions for further study that we are quite frankly over-
whelmed by the enormity of the job that must be done. We
hope that this book will serve to interest other people, in many
fields of study and in many countries of the world, to raise the
space and time horizons of their concerns and to join us in
understanding and preparing for a period of great transition —
the transition from growth to global equilibrium.

CHAPTER I

THE

NATURE
OF

EXPONENTIAL
GROWTH

People at present think that five sons
are not too many and each son has five
sons also, and before the death of the
grandfather there are already 25
descendants. Therefore people are
more and wealth is less; they work
hard and receive little.

HAN FEI-TZU, ca. 500 B.C.

All five elements basic to the study
reported here— population, food production, industrialization,
pollution, and consumption of nonrenewable natural re-
sources — are increasing. The amount of their increase each year
follows a pattern that mathematicians call exponential growth.
Nearly all of mankind's current activities, from use of fertilizer
to expansion of cities, can be represented by exponential growth
curves (see figures 2 and 3). Since much of this book deals
with the causes and implications of exponential growth curves,
it is important to begin with an understanding of their general
characteristics.

THE MATHEMATICS OF EXPONENTIAL GROWTH

Most people are accustomed to thinking of growth as a linear
process. A quantity is growing linearly when it increases by a

THE NATURE OF EXPONENTIAL GROWTH

Figure 2 WORLD FERTILIZER CONSUMPTION

thousand metric Ions

50,000

40.000

30.000

20.000

1 i

>•

phi

jsphat

_ — - 1

^ P

•lash

1938 1*40 1942 1*44 1*44 1*4* 1950 1952 1*54 1956 1958 1960 1962 1964 1966 1968 1*70

World fertilizer consumption Is increasing exponentially, with a doubling
time ol about 10 years. Total use is now five times greater than It was
during World War II.

NOTE: Figures do not include (he USSR or the People's Republic of Chin*.
SOURCES: UN Department of Economic and Social Affair*. Statistical yearbook 7955.
Statistical Yearbook 196V. and Statistical Yeart>oo* 7970 (Now York: United Nation*, 1056.
1981. and 1971).

constant amount in a constant time period. For example, a
child who becomes one inch taller each year is growing lin-
early. If a miser hides $10 each year under his mattress, his

THE NATURE OF EXPONENTIAL GROWTH

Figure 3 WORLD URBAN POPULATION

millions ot people

2000

1500

1000

less

Jeveloped re

gions /

^ more d€

veloped rec

ions

1950 1960 1970 1990 1990

Total urban population is expected to increase exponentially in the less
developed regions of the world, but almost linearly in the more developed
regions. Present average doubling time tor city populations in less de-
veloped regions is 15 years.

SOURCE: UN Department of Economic end Social AHairs, The World Population Situation
In 1970 (New York: United Nations, 1971).

horde of money is also increasing in a linear way. The amount
of increase each year is obviously not affected by the size of
the child nor the amount of money already under the mattress.

A quantity exhibits exponential growth when it increases
by a constant percentage of the whole in a constant time
period. A colony of yeast cells in which each cell divides into
two cells every 10 minutes is growing exponentially. For each
single cell, after 10 minutes there will be two cells, an increase

THE NATURE OF EXPONENTIAL GROWTH

Figure 4 THE GROWTH OF SAVINGS

dollars

/
1

($1

exponent!
X) invested at

al growth —
r% interest) f

1
/

1—

one d o u b I i n q

time
r is ,

($1

inear growth
0/year under t

ie mattress*

1400

1000

200

time (years) 10

II a miser hides $10 each year under his mattress, his savings will grow
linearly, as shown by the lower curve. If, after 10 years, he invests his
$100 at 7 percent interest, that $100 will grow exponentially, with a
doubling time of 10 years.

of 100 percent. After the next 10 minutes there will be four
cells, then eight, then sixteen. If a miser takes $100 from his
mattress and invests it at 7 percent (so that the total amount
accumulated increases by 7 percent each year), the invested
money will grow much faster than the linearly increasing
stock under the mattress (see figure 4). The amount added
each year to a bank account or each 10 minutes to a yeast
colony is not constant. It continually increases, as the total
accumulated amount increases. Such exponential growth is a
common process in biological, financial, and many other sys-
tems of the world.

THE NATURE OF EXPONENTIAL GROWTH

Common as it is, exponential growth can yield surprising
results— results that have fascinated mankind for centuries.
There is an old Persian legend about a clever courtier who
presented a beautiful chessboard to his king and requested
that the king give him in return 1 grain of rice for the first
square on the board, 2 grains for the second square, 4 grains
for the third, and so forth. The king readily agreed and or-
dered rice to be brought from his stores. The fourth square
of the chessboard required 8 grains, the tenth square took 512
grains, the fifteenth required 16384, and the twenty-first
square gave the courtier more than a million grains of rice.
By the fortieth square a million million rice grains had to be
brought from the storerooms. The king's entire rice supply
was exhausted long before he reached the sixty-fourth square.
Exponential increase is deceptive because it generates immense
numbers very quickly.

A French riddle for children illustrates another aspect of
exponential growth— the apparent suddenness with which it
approaches a fixed limit. Suppose you own a pond on which a
water lily is growing. The lily plant doubles in size each day.
If the lily were allowed to grow unchecked, it would com-
pletely cover the pond in 30 days, choking off the other forms
of life in the water. For a long time the lily plant seems small,
and so you decide not to worry about cutting it back until
it covers half the pond. On what day will that be? On the
twenty-ninth day, of course. You have one day to save your
pond*

It is useful to think of exponential growth in terms of
doubling time, or the time it takes a growing quantity to

* We are indebted to M. Robert Lattes for telling us this riddle.

THE NATURE OF EXPONENTIAL GROWTH

double in size. In the case of the lily plant described above,
the doubling time is 1 day. A sum of money left in a bank
at 7 percent interest will double in 10 years. There is a simple
mathematical relationship between the interest rate, or rate
of growth, and the time it will take a quantity to double in
size. The doubling time is approximately equal to 70 divided
by the growth rate, as illustrated in table 1.

Table 1 DOUBLING TIME

Growth rate

Doubling time

(% per year)

(yean)

0.1

700

0.5

140

1.0

2.0

4.0

5.0

7.0

10.0

MODELS AND EXPONENTIAL GROWTH

Exponential growth is a dynamic phenomenon, which means
that it involves elements that change over time. In simple
systems, like the bank account or the lily pond, the cause of
exponential growth and its future course are relatively easy to
understand. When many different quantities are growing
simultaneously in a system, however, and when all the quan-
tities are interrelated in a complicated way, analysis of the
causes of growth and of the future behavior of the system
becomes very difficult indeed. Does population growth cause
industrialization or does industrialization cause population
growth? Is either one singly responsible for increasing pol-

THE NATURE OF EXPONENTIAL GROWTH

lution, or are they both responsible? Will more food produc-
tion result in more population? If any one of these elements
grows slower or faster, what will happen to the growth rates
of all the others? These very questions are being debated in
many parts of the world today. The answers can be found
through a better understanding of the entire complex system
that unites all of these important elements.

Over the course of the last 30 years there has evolved at
the Massachusetts Institute of Technology a new method for
understanding the dynamic behavior of complex systems. The
method is called System Dynamics.* The basis of the method
is the recognition that the structure of any system — the many
circular, interlocking, sometimes time-delayed relationships
among its components — is often just as important in deter-
mining its behavior as the individual components themselves.
The world model described in this book is a System Dynamics
model.

Dynamic modeling theory indicates that any exponentially
growing quantity is somehow involved with a positive feed-
back loop. A positive feedback loop is sometimes called a
"vicious circle." An example is the familiar wage-price spiral —
wages increase, which causes prices to increase, which leads to
demands for higher wages, and so forth. In a positive feedback
loop a chain of cause-and-effect relationships closes on itself,
so that increasing any one element in the loop will start a
sequence of changes that will result in the originally changed
element being increased even more.

* A detailed description of the method of System Dynamics analysis is
presented in J. W. Forrester's Industrial Dynamics (Cambridge, Mass.:
MIT Press, 1961) and Principles of Systems ('Cambridge, Mass.: Wright-
Allen Press, 1968).

THE NATURE OF EXPONENTIAL GROWTH

The positive feedback loop that accounts for exponential
increase of money in a bank account can be represented like
this:

interest added
(dollars per year)

money in account
(dollars)

Suppose $100 is deposited in the account. The first year's
interest is 7 percent of $100, or $7, which is added to the
account, making the total $107. The next year's interest is 7
percent of $107, or $7.49, which makes a new total of $114.49.
One year later the interest on that amount will be more than
$8.0p. The more money there is in the account, the more
money will be added each year in interest. The more is added,
the more there will be in the account the next year causing
even more to be added in interest. And so on. As we go
around and around the loop, the accumulated money in the
account grows exponentially. The rate of interest (constant
at 7 percent) determines the gain around the loop, or the
rate at which the bank account grows.

We can begin our dynamic analysis of the long-term world
situation by looking for the positive feedback loops underlying
the exponential growth in the five physical quantities we have
already mentioned. In particular, the growth rates of two of
these elements — population and industrialization — are of in-
terest, since the goal of many development policies is to
encourage the growth of the latter relative to the former. The

THE NATURE OF EXPONENTIAL GROWTH

Figure 5 WORLD POPULATION

billions ol people

1650 1700 1750 1800 1850 1900 1950 2000

World population since 1650 has been growing exponentially at an increas-
ing rate. Estimated population in 1970 Is already slightly higher than the
protection illustrated here (which was made in 1958). The present world
population growth rate is about 2.1 percent per year, corresponding to a
doubling time ol 33 years.

SOURCE: Donald J. Bogue, Principles ol Demography (New York: John Wiley and Sons,
1969).

two basic positive feedback loops that account for exponential
population and industrial growth are simple in principle. We
will describe their basic structures in the next few pages. The
many interconnections between these two positive feedback
loops act to amplify or to diminish the action of the loops,
to couple or uncouple the growth rates of population and of
industry. These interconnections constitute the rest of the world
model and their description will occupy much of the rest of
this book.

THE NATURE OF EXPONENTIAL GROWTH

WORLD POPULATION GROWTH

The exponential growth curve of world population is shown
in figure 5. In 1650 the population numbered about 0.5 billion,*
and it was growing at a rate of approximately 0.3 percent per
year. 1 That corresponds to a doubling time of nearly 250 years.
In 1970 the population totaled 3.6 billion and the rate of growth
was 2.1 percent per year. 2 The doubling time at this growth
rate is 33 years. Thus, not only has the population been grow-
ing exponentially, but the rate of growth has also been growing.
We might say that population growth has been "super"-
exponential; the population curve is rising even faster than it
would if growth were strictly exponential.

The feedback loop structure that represents the dynamic
behavior of population growth is shown below.

(+)

births
per year

average fertility
(fraction of population
giving birth each year)

population

(-)

deaths
per year

average mortality
(fraction of population
dying each year)

On the left is the positive feedback loop that accounts for
the observed exponential growth. In a population with constant
average fertility, the larger the population, the more babies
will be born each year. The more babies, the larger the popula-

•The word "billion" in this book will be used to mean 1000 million,
ije. the European "milliard."
1 Notes begin on page 201.

THE NATURE OF EXPONENTIAL GROWTH

tion will be the following year. After a delay to allow those
babies to grow up and become parents, even more babies will
be born, swelling the population still further. Steady growth
will continue as long as average fertility remains constant. If,
in addition to sons, each woman has on the average two
female children, for example, and each of them grows up to
have two more female children, the population will double
each generation. The growth rate will depend on both the
average fertility and the length of the delay between genera-
tion's. Fertility is not necessarily constant, of course, and in
chapter III we will discuss some of the factors that cause it
to vary.

There is another feedback loop governing population
growth, shown on the right side of the diagram above. It is a
negative feedbac\ loop. Whereas positive feedback loops
generate runaway growth, negative feedback loops tend to
regulate growth and to hold a system in some stable state.
They behave much as a thermostat does in controlling the
temperature of a room. If the temperature falls, the thermostat
activates the heating system, which causes the temperature to
rise again. When the temperature reaches its limit, the ther-
mostat cuts off the heating system, and the temperature begins
to fall again. In a negative feedback loop a change in one
clement is propagated around the circle until it comes back to
change that element in a direction opposite to the initial
change.

The negative feedback loop controlling population is based
upon average mortality, a reflection of the general health of
the population. The number of deaths each year is equal to
the total population times the average mortality (which we
might think of as the average probability of death at any age).

THE NATURE OF EXPONENTIAL GROWTH

An increase in the size of a population with constant average
mortality will result in more deaths per year. More deaths will
leave fewer people in the population, and so there will be
fewer deaths the next year. If on the average 5 percent of the
population dies each year, there will be 500 deaths in a popula-
tion of 10,000 in one year. Assuming no births for the moment,
that would leave 9,500 people the next year. If the probability
of death is still 5 percent, there will be only 475 deaths in
this smaller population, leaving 9,025 people. The next year
there will be only 452 deaths. Again, there is a delay in this
feedback loop because the mortality rate is a function of the
average age of the population. Also, of course, mortality even
at a given age is not necessarily constant.

If there were no deaths in a population, it would grow
exponentially by the positive feedback loop of births, as shown
below. If there were no births, the population would decline

time

to zero because of the negative feedback loop of deaths, also
as shown below. Since every real population experiences both

THE NATURE OF EXPONENTIAL GROWTH

births and deaths, as well as varying fertility and mortality, the
dynamic behavior of populations governed by these two
interlocking feedback loops can become fairly complicated.

What has caused the recent super-exponential rise in world
population ? Before the industrial revolution both fertility and
mortality were comparatively high and irregular. The birth
rate generally exceeded the death rate only slightly, and popu-
lation grew exponentially, but at a very slow and uneven rate.
In 1650 the average lifetime of most populations in the world
was only about 30 years. Since then, mankind has developed
many practices that have had profound effects on the popula-
tion growth system, especially on mortality rates. With the
spread of modern medicine, public health techniques, and new
methods of growing and distributing foods, death rates have
fallen around the world. World average life expectancy is
currently about 53 years 3 and still rising. On a world average
the gain around the positive feedback loop (fertility) has
decreased only slightly while the gain around the negative
feedback loop (mortality) is decreasing. The result is an
increasing dominance of the positive feedback loop and the
sharp exponential rise in population pictured in figure 5.

What about the population of the future? How might we
extend the population curve of figure 5 into the twenty-first
century? We will have more to say about this in chapters
III and IV. For the moment we can safely conclude that
because of the delays in the controlling feedback loops, espe-
cially the positive loop of births, there is no possibility of
leveling off the population growth curve before the year 2000,
even with the most optimistic assumption of decreasing fer-
tility. Most of the prospective parents of the year 2000 have
already been born. Unless there is a sharp rise in mortality,

THE NATURE OF EXPONENTIAL GROWTH

Figure 6 WORLD INDUSTRIAL PRODUCTION

world industrial production- index (1963=100)

total .

/ /
/ 1"
//

per capita -jy'

/—-- - /

1930 1940 1950 19S0 1970

World industrial production, relative to the base year 1963, also shows a
clear exponential increase despite small fluctuations. The 1963-68 average
growth rate of total production is 7 percent per year. The per capita growth
rate is 5 percent per year.

SOURCES: UN Department of Economic and Social Affairs, Statistical Yearbook 1956 and
Statistical Yearbook 1969 (New Yortc: United Nations, 1957 and 1970).

which mankind will certainly strive mightily to avoid, we
can look forward to a world population of around 7 billion
persons in 30 more years. And if we continue to succeed in
lowering mortality with no better success in lowering fertility
than we have accomplished in the past, in 60 years there will
be four people in the world for every one person living today.

WORLD ECONOMIC GROWTH

A second quantity that has been increasing in the world even
faster than human population is industrial output. Figure 6

THE NATURE OF EXPONENTIAL GROWTH

shows the expansion of world industrial production since 1930,
with 1963 production as the base of reference. The average
growth rate from 1963 to 1968 was 7 percent per year, or
5 percent per year on a per capita basis.

What is the positive feedback loop that accounts for expo-
nential growth of industrial output? The dynamic structure,
diagramed below, is actually very similar to the one we have
already described for the population system.

(-) depreciation
(capital discarded
per year)

lifetime
of capital

With a given amount of industrial capital (factories, trucks,
tools, machines, etc.), a certain amount of manufactured out-
put each year is possible. The output actually produced is also
dependent on labor, raw materials, and other inputs. For the
moment we will assume that these other inputs are sufficient,
so that capital is the limiting factor in production. (The world
model docs include these other inputs.) Much of each year's
output is consumable goods, such as textiles, automobiles, and
houses, that leave the industrial system. But some fraction of
the production is more capital — looms, steel mills, lathes —
which is an investment to increase the capital stock. Here we
have another positive feedback loop. More capital creates more

THE NATURE OF EXPONENTIAL GROWTH

Figure 7 ECONOMIC GROWTH RATES

GNP per capita (US dollars per person per year) . us

•

2000
1500

United Kir

gdom

1000
500
0

1 Japan

_» Ghana

1750 1800 1850 1900 1950 2000

The economic growth of individual nations indicates that differences in
exponential growth rates are widening the economic gap between rich and
poor countries.

SOURCE: Simon Kuznets. Economic Growth ol Nations (Cambridge, Mass.: Harvard Uni-
versity Press, 1971).

THE NATURE OF EXPONENTIAL GROWTH

output, some variable fraction of the output is investment,
and more investment means more capital. The new, larger
capital stock generates even more output, and so on. There
are also delays in this feedback loop, since the production of a
major piece of industrial capital, such as an electrical generat-
ing plant or a refinery, can take several years.

Capital stock is not permanent. As capital wears out or
becomes obsolete, it is discarded. To model this situation we
must introduce into the capital system a negative feedback
loop accounting for capital depreciation. The more capital
there is, the more wears out on the average each year; and the
more that wears out, the less there will be the next year. This
negative feedback loop is exactly analogous to the death rate
loop in the population system. As in the population system,
the positive loop is strongly dominant in the world today,
and the world's industrial capital stock is growing exponen-
tially.

Since industrial output is growing at 7 percent per year
and population only at 2 percent per year, it might appear
that dominant positive feedback loops are a cause for rejoicing.
Simple extrapolation of those growth rates would suggest that
the material standard of living of the world's people will
double within the next 14 years. Such a conclusion, however,
often includes the implicit assumption that the world's growing
industrial output is evenly distributed among the world's
citizens. The fallacy of this assumption can be appreciated
when the per capita economic growth rates of some individual
nations are examined (see figure 7).

Most of the world's industrial growth plotted in figure 6 is
actually taking place in the already industrialized countries,
where the rate of population growth is comparatively low.

THE NATURE OF EXPONENTIAL GROWTH

Table 2 ECONOMIC AND POPULATION GROWTH RATES

Average

annual

growth rate

GNP

of GNP

Population

of population

per capita

(1968)

(1961-68)

(1968)

(1961-68)

Country

( million )

(% per year)

(US dollars)

( % per year)

People's Republic

of China*

730

1.5

0.3

India

524

2.5

100

1.0

USSR *

238

1.3

1,100

5.8

United States

201

1.4

3,980

3.4

Pakistan ...

123

2.6

100

3.1

Indonesia -

113

2.4

100

0.8

Japan

101

1.0

1,190

9.9

Brazil

3.0

250

1.6

Nigeria

2.4

— 0.3

Federal Republic

of Germany

1.0

1,970

3.4

* The International Bank for Reconstruction and Development qualifies its estimates
for China and the USSR with the following statement: "Estimates of GNP per
capita and its growth rate have a wide margin of error mainly because of the
problems in deriving the GNP at factor cost from net material product and in
converting the GNP estimate into US dollars." United Nations estimates are in
general agreement with those of the IBRD.

source: World Banh Atlas (Washington.DC: International Bank for Reconstruction
and Development, 1970).

The most revealing possible illustration of that fact is a simple
table listing the economic and population growth rates of the
ten most populous nations of the world, where 64 percent
of the world's population currently lives. Table 2 makes very
clear the basis for the saying, "The rich get richer and the poor
get children."

It is unlikely that the rates of growth listed in table 2 will
continue unchanged even until the end of this century. Many

THE NATURE OF EXPONENTIAL GROWTH

factors will change in the next 30 years. The end of civil
disturbance in Nigeria, for example, will probably increase the
economic growth rate there, while the onset of civil disturb-
ance and then war in Pakistan has already interfered with
economic growth there. Let us recognize, however, that the
growth rates listed above are the products of a complicated
social and economic system that is essentially stable and that
is likely to change slowly rather than quickly, except in cases
of severe social disruption.

It is a simple matter of arithmetic to calculate extrapolated
values for gross national product (GNP) per capita from now
until the year 2000 on the assumption that relative growth
rates of population and GNP will remain roughly the same in
these ten countries. The result of such a calculation appears in
table 3. The values shown there will almost certainly not ac-
tually be realized. They are not predictions. The values merely
indicate the general direction our system, as it is currently
structured, is taking us. They demonstrate that the process of

Table 3 EXTRAPOLATED GNP FOR THE YEAR 2000

GNP per capita

Country (in VS dollars •)

People's Republic of China 100

India 140

USSR 6,330

United States 11,000

Pakistan 250

Indonesia 130

Japan 23,200

Brazil 440

Nigeria 60

Federal Republic of Germany 5,850

• Based on the 1968 dollar with no allowance for inflation.

THE NATURE OF EXPONENTIAL GROWTH

economic growth, as it is occurring today, is inexorably widen-
ing the absolute gap between the rich and the poor nations of
the world.

Most people intuitively and correctly reject extrapolations
like those shown in table 3, because the results appear ridicu-
lous. It must be recognized, however, that in rejecting extra-
polated values, one is also rejecting the assumption that there
will be no change in the system. If the extrapolations in table 3
do not actually come to pass, it will be because the balance
between the positive and negative feedback loops determining
the growth rates of population and capital in each nation has
been altered. Fertility, mortality, the capital investment rate,
the capital depreciation rate — any or all may change. In pos-
tulating any different outcome from the one shown in table 3,
one must specify which of these factors is likely to change,
by how much, and when. These are exactly the questions we
are addressing with our model, not on a national basis, but
on an aggregated global one.

To speculate with any degree of realism on future growth
rates of population and industrial capital, we must know
something more about the other factors in the world that
interact with the population-capital system. We shall begin
by asking a very basic set of questions.

Can the growth rates of population and capital presented
in table 3 be physically sustained in the world? How many
people can be provided for on this earth, at what level of
wealth, and for how long? To answer these questions, we
must look in detail at those systems in the world which pro-
vide the physical support for population and economic growth.

CHAPTER II

THE

LIMITS

EXPONENTIAL
GROWTH

For which of you, intending to build a
tower, sitteth not down first, and
counteth the cost, whether he have
sufficient to finish it?

LUKE 14:28

What will be needed to sustain
world economic and population growth until, and perhaps
even beyond, the year 2000? The list of necessary ingredients
is long, but it can be divided roughly into two main categories.

The first category includes the physical necessities that sup-
port all physiological and industrial activity — food, raw mate-
rials, fossil and nuclear fuels, and the ecological systems of
the planet which absorb wastes and recycle important basic
chemical substances. These ingredients are in principle tan-
gible, countable items, such as arable land, fresh water, metals,
forests, the oceans. In this chapter we will assess the world's
stocks of these physical resources, since they are the ultimate
determinants of the limits to growth on this earth.

The second category of necessary ingredients for growth
consists of the social necessities. Even if the earth's physical
systems are capable of supporting a much larger, more econom-

THE LIMITS TO EXPONENTIAL GROWTH

ically developed population, the actual growth of the economy
and of the population will depend on such factors as peace
and social stability, education and employment, and steady
technological progress. These factors are much more difficult
to assess or to predict. Neither this book nor our world model
at this stage in its development can deal explicitly with these
social factors, except insofar as our information about the
quantity and distribution of physical supplies can indicate
possible future social problems.

Food, resources, and a healthy environment are necessary
but not sufficient conditions for growth. Even if they are abun-
dant, growth may be stopped by social problems. Let us assume
for the moment, however, that the best possible social con-
ditions will prevail. How much growth will the physical system
then support? The answer we obtain will give us some esti-
mate of the upper limits to population and capital growth,
but no guarantee that growth will actually proceed that far.

FOOD

In Zambia, in Africa, 260 of every thousand babies born are dead
before their first birthday. In India and Pakistan the ratio is 140 of
every thousand; in Colombia it is 82. Many more die before they reach
school age; others during the early school years.

Where death certificates are issued for preschool infants in the poor
countries, death is generally attributed to measles, pneumonia, dysen-
tery, or some other disease. In fact these children are more likely to be
the victims of malnutrition. 4

No one knows exactly how many of the world's people are
inadequately nourished today, but there is general agreement
that the number is large— perhaps 50 to 60 percent of the
population of the less industrialized countries, 5 which means
one-third of the population of the world. Estimates by the

THE LIMITS TO EXPONENTIAL GROWTH

Figure 8 PROTEIN AND CALORIC INTAKE

protein required calories required.

100 80 60 4 0 20 0 1000 2000 3000

grams of protein per capita per day calories per capita per day

= other protein supply K83 animal protein supply m calorie supply

Daily protein and calorie requirements are not being supplied to most
areas of the world. Inequalities ol distribution exist not only among
regions, as shown here, but also within regions. According to the UN Food
and Agriculture Organization, areas of greatest shortage include the

THE LIMITS TO EXPONENTIAL GROWTH

"Andean countries, the semi-arid stretches ol Africa and the Near East,
and some densely populated countries oi Asia." Lines indicating calories
and proteins required are those estimated tor North Americans. The as-
sumption has been made that it diets in other regions were sufficient to
allow people to reach full potential body weight, requirements would be
the same everywhere.

SOURCE: UN Food and Agriculture Organization, Provisional Indicative World Plan tor
Agricultural Development (Rome: UN Food and Agriculture Organization, 1970).

UN Food and Agriculture Organization (FAO) indicate that
in most of the developing countries basic caloric requirements,
and particularly protein requirements, are not being supplied
(see figure 8). Furthermore, although total world agricultural
production is increasing, food production per capita in the
nonindustrialized countries is barely holding constant at its
present inadequate level (see figure 9). Do these rather dismal
statistics mean that the limits of food production on the earth
have already been reached?

The primary resource necessary for producing food is land.
Recent studies indicate that there are, at most, about 3.2 billion
hectares of land (7.86 billion acres) potentially suitable for
agriculture on the earth. 6 Approximately half of that land,
the richest, most accessible half, is under cultivation today.
The remaining land will require immense capital inputs to
reach, clear, irrigate, or fertilize before it is ready to produce
food. Recent costs of developing new land have ranged from
$215 to $5,275 per hectare. Average cost for opening land in
unsettled areas has been $1,150 per hectare. 7 According to an
FAO report, opening more land to cultivation is not econom-
ically feasible, even given the pressing need for food in the
world today:

In Southern Asia ... in some countries in Eastern Asia, in the Near
East and North Africa, and in certain parts of Latin America and
Africa . . . there is almost no scope for expanding the arable area.

THE LIMITS TO EXPONENTIAL GROWTH

Figure 9 FOOD PRODUCTION

regional average food production index (1952 - 56 = 100.)
Africa Near East

1958 1960 1962 1964 1966 1968 1970 1958 1960 1962 1964 1966 1968

Far East Latin America

1958 1960 1962 1964 1966 1968 1970 1958 1960 1962 1964 1966 1968

_ total food production a per capita food production

Total food production in the nonindustrialized regions of the world has
risen at about the same rate as the population. Thus tood production
per capita has remained nearly constant, at a low level.

SOURCE: UN Food and Agriculture Organization. The Stale ol Food and Agriculture 1970
(Rome: UN Food and Agriculture Organization, 1970).

. . . In the dryer regions it will even be necessary to return to perma-
nent pasture the land which is marginal or submarginal for cultivation.
In most of Latin America and Africa South of the Sahara there are
still considerable possibilities for expanding cultivated area, but the costs
of development are high and it will be often more economical to inten-
sify utilization of the areas already settled. 8

If the world's people did decide to pay the high capital costs,
to cultivate all possible arable land, and to produce as much
food as possible, how many people could theoretically be fed ?

THE LIMITS TO EXPONENTIAL GROWTH

Figure 10 ARABLE LAND

billion hectares

1650 1700 1750 1800 1850 1900 1950 2000 2050 2100

Total world supply of arable land is about 3.2 billion hectares. About 0.4
hectares per person ot arable land are needed at present productivity. The
curve ot land needed thus reflects the population growth curve. The
light line after 1970 shows the projected need for land, assuming that
world population continues to grow at its present rate. Arable land
available decreases because arable land is removed for urban-industrial
use as population grows. The dotted curves show land needed if present
productivity is doubled or quadrupled.

The lower curve in figure 10 shows the amount of land needed
to feed the growing world population, assuming that the
present world average of 0.4 hectares per person is sufficient.
(To feed the entire world population at present US standards,
0.9 hectares per person would be required.) The upper curve in
figure 10 shows the actual amount of arable land available
over time. This line, slopes downward because each additional
person requires a certain amount of land (0.08 hectares per

THE LIMITS TO EXPONENTIAL GROWTH

person assumed here*) for housing, roads, waste disposal,
power lines, and other uses that essentially "pave" arable land
and make it unusable for food production. Land loss through
erosion is not shown here, but it is by no means negligible.
Figure 10 shows that, even with the optimistic assumption that
all possible land is utilized, there will still be a desperate land
shortage before the year 2000 if per capita land requirements
and population growth rates remain as they are today.

Figure 10 also illustrates some very important general facts
about exponential growth within a limited space. First, it
shows how one can move within a very few years from a
situation of great abundance to one of great scarcity. There
has been an overwhelming excess of potentially arable land
for all of history, and now, within 30 years (or about one
population doubling time), there may be a sudden and serious
shortage. Like the owner of the lily pond in our example in
chapter I, the human race may have very little time to react
to a crisis resulting from exponential growth in a finite space.

A second lesson to be learned from figure 10 is that precise
numerical assumptions about the limits of the earth are un-
important when viewed against the inexorable progress of
exponential growth. We might assume, for example, that no
arable land is taken for cities, roads, or other nonagricultural
uses. In that case, the land available is constant, as shown by
the horizontal dashed line. The point at which the two curves
cross is delayed by about 10 years. Or we can suppose that it
is possible to double, or even quadruple, the productivity of
the land through advances in agricultural technology and in-

* Aerial surveys of forty-four counties in the western United States
from 1950 to 1960 indicate that built-on land ranged from .008 to .174
hectares per person. 9

THE LIMITS TO EXPONENTIAL GROWTH

vestments in capital, such as tractors, fertilizer, and irrigation
systems. The effects of two different assumptions about in-
creased productivity are shown by the dotted lines in figure
10. Each doubling of productivity gains about 30 years, or
less than one population doubling time.

Of course, society will not be suddenly surprised by the
"crisis point" at which the amount of land needed becomes
greater than that available. Symptoms of the crisis will begin
to appear long before the crisis point is reached. Food prices
will rise so high that some people will starve; others will be
forced to decrease the effective amount of land they use and
shift to lower quality diets. These symptoms are already appar-
ent in many parts of the world. Although only half the land
shown in figure 10 is now under cultivation, perhaps 10 to 20
million deaths each year can be attributed directly or indirectly
to malnutrition. 10

There is no question that many of these deaths are due to
the world's social limitations rather than its physical ones.
Yet there is clearly a link between these two kinds of limitations
in the food-producing system. If good fertile land were still
easily reached and brought under cultivation, there would be no
economic barrier to feeding the hungry, and no difficult social
choices to make. The best half of the world's potentially arable
land is already cultivated, however, and opening new land
is already so costly that society has judged it "uneconomic."
This is a social problem exacerbated by a physical limitation.

Even if society did decide to pay the necessary costs to gain
new land or to increase productivity of the land already cul-
tivated, figure 10 shows how quickly rising population would
bring about another "crisis point." And each successive crisis
point will cost more to overcome. Each doubling of yield

THE LIMITS TO EXPONENTIAL GROWTH

from the land will be more expensive than the last one. We
might call this phenomenon the law of increasing costs. The
best and most sobering example of that law comes from an
assessment of the cost of past agricultural gains. To achieve a
34 percent increase in world food production from 1951 to 1966,
agriculturalists increased yearly expenditures on tractors by 63
percent, annual investment in nitrate fertilizers by 146 percent,
and annual use of pesticides by 300 percent. 11 The next 34 per-
cent increase will require even greater inputs of capital and
resources.

How many people can be fed on this earth? There is, of
course, no simple answer to this question. The answer depends
on the choices society makes among various available alterna-
tives. There is a direct trade-off between producing more food
and producing other goods and services needed or desired by
mankind. The demand for these other goods and services is
also increasing as population grows, and therefore the trade-
off becomes continuously more apparent and more difficult to
resolve. Even if the choice were consistently to produce food
as the first priority, however, continued population growth
and the law of increasing costs could rapidly drive the system
to the point where all available resources were devoted to
producing food, leaving no further possibility of expansion.

In this section we have discussed only one possible limit to
food production — arable land. There are other possible limits,
but space does not permit us to discuss them in detail here.
The most obvious one, second in importance only to land, is
the availability of fresh water. There is an upper limit to the
fresh water runoff from the land areas of the earth each year,
and there is also an exponentially increasing demand for that
water. We could draw a graph exactly analogous to figure 10

THE LIMITS TO EXPONENTIAL GROWTH

to show the approach of the increasing demand curve for
water to the constant average supply. In some areas of the
world, this limit will be reached long before the land limit
becomes apparent.

It is also possible to avoid or extend these limits by techno-
logical advances that remove dependence on the land (syn-
thetic food) or that create new sources of fresh water (desalin-
ization of sea water). We shall discuss such innovations fur-
ther in chapter IV. For the moment it is sufficient to recognize
that no new technology is spontaneous or without cost. The
factories and raw materials to produce synthetic food, the
equipment and energy to purify sea water must all come from
the physical world system.

The exponential growth of demand for food results directly
from the positive feedback loop that is now determining the
growth of human population. The supply of food to be ex-
pected in the future is dependent on land and fresh water and
also on agricultural capital, which depends in turn on the
other dominant positive feedback loop in the system — the
capital investment loop. Opening new land, farming the sea,
or expanding use of fertilizers and pesticides will require an
increase of the capital stock devoted to food production. The
resources that permit growth of that capital stock tend not
to be renewable resources, like land or water, but nonrenewable
resources, like fuels or metals. Thus the expansion of food pro-
duction in the future is very much dependent on the avail-
ability of nonrenewable resources. Are there limits to the
earth's supply of these resources?

NONRENEWABLE RESOURCES

Even taking into account such economic factors as increased prices
with decreasing availability, it would appear at present that the quanti-

THE LIMITS TO EXPONENTIAL GROWTH

ties of platinum, gold, zinc, and lead are not sufficient to meet demands.
At the present rate of expansion . . . silver, tin, and uranium may be in
short supply even at higher prices by the turn of the century. By the
year 2050, several more minerals may be exhausted if the current rate
of consumption continues.

Despite spectacular recent discoveries, there are only a limited num-
ber of places left to search for most minerals. Geologists disagree about
the prospects for finding large, new, rich ore deposits. Reliance on such
discoveries would seem unwise in the long term. 12

Table 4 lists some of the more important mineral and fuel
resources, the vital raw materials for today's major industrial
processes. The number following each resource in column 3
is the static reserve index, or the number of years present
known reserves of that resource (listed in column 2) will last
at the current rate of usage. This static index is the measure
normally used to express future resource availability. Under-
lying the static index are several assumptions, one of which
is that the usage rate will remain constant.

But column 4 in table 4 shows that the world usage rate
of every natural resource is growing exponentially. For many
resources the usage rate is growing even faster than the popu-
lation, indicating both that more people are consuming
resources each year and also that the average consumption per
person is increasing each year. In other words, the exponential
growth curve of resource consumption is driven by both the
positive feedback loops of population growth and of capital
growth.

We have already seen in figure 10 that an exponential in-
crease in land use can very quickly run up against the fixed
amount of land available. An exponential increase in resource
consumption can rapidly diminish a fixed store of resources
in the same way. Figure 11, which is similar to figure 10, illus-

THE LIMITS TO EXPONENTIAL GROWTH

Table 4 NONRENEWABLE NATURAL RESOURCES

1 2 3 4 5 6

Exponen-
tial Index

„ _ _ _ „ Calculated

Known Static Protected Rate Exponen-

Resource Global Index of Growth tial Index ; fimes

Reserves' (years)" (% per Year)' (years)'' K „' own

High Av. Low Reserves

(years) '

Aluminum

1.17X10° tons'

100

7.7

6.4

5.1

Chromium

7.75 X10 8 tons

420

3.3

2.6

2.0

154

Coal

5X10 12 tons

2300

5.3

4.1

3.0 k

111

150

Cobalt

4.8 X10 9 lbs

110

2.0

1.5

1.0

148

Copper

j\jo a iu ions

J.O

4 6

4ft

Gold

353 X 10 s troy oz

4.8

4.1

3.4'

Iron

1 X 10 11 tons

240

2.3

1.8

1.3

173

Lead

91 X 10 6 tons

2.4

2.0

1.7

Manganese

8X10 8 tons

3.5

2.9

2.4

Mercury

334 X 10" flasks

3.1

2.6

2.2

THE LIMITS TO EXPONENTIAL GROWTH

Countries or Areas
with Highest Reserves
(% of world total)'

Prime Producers

i rrf t ilia

(% of world total)'

Prime Consumers
(% of world total)'

US Con-
sumption
as % of
World
Total 1

Australia (33)
v. lUinca l^U )
Jamaica (10)

Jamaica (19)
Surinam (12)

US (42)
USSR (12)

Rep. of S. Africa (75)

TTCCR /\(\\
UMK (jK) )

Turkey (10)

US (32)

USSR (20)

Rep. of Congo (31)

/-uniDia V

Rep. of Congo (51)

US (28)
Chile (19)

US (20)
USSR (15)

A.unnia \ Ij )

US (33)
USSR (13)
Japan (11)

Rep. of S. Africa (40)

Rep. of S.Africa (77)
Canada (6)

USSR (33)
S. Am. (18)
Canada (14)

USSR (25)
US (14)

US (28)

USSR (24)

W. Germany (7)

US (39)

USSR (13)
Australia (13)
Canada (11)

US (25)

USSR (13)

W. Germany (11)

Rep. of S. Africa (38) USSR (34)
USSR (25) Brazil (13)

Rep. of S. Africa (13)

Spain (30)
Italy (21)

Spain (22)
Italy (21)
USSR (18)

THE LIMITS TO EXPONENTIAL GROWTH

1 2 3 4 5 6

Exponen-
tial Index

mm Calculated

Known Static Projected Rate Exponen-

Resource Global Index of Growth tial Index

Reserves' (years)" (% per Year)' (years)' 3 ''™'

High Av. Low Reserves
(years)

Molybdenum

10.8 X10 9 lbs

5.0

4.5

4.0

Natural Gas

1.14X10 15 cu ft

5.5

4.7

3.9

Nickel

147X10° lbs

150

4.0

3.4

2.8

Petroleum

455 X10 9 bbls

4.9

3.9

2.9

Platinum
Group "

429 X10 6 troy oz

130

4.5

3.8

3.1

Silver

5.5 X10 9 troy oz

4.0

2.7

1.5

Tin

4.3 X 10 s lg tons

1.1

Tungsten

2.9X10 9 lbs

2.9

2.5

2.1

Zinc

123X10 8 tons

2.9

2.5

THE LIMITS TO EXPONENTIAL GROWTH

Countries or Areas
with Highest Reserves
(% of world total)'

Prime Producers
(% of world total)'

Prime Consumers
(% of world total)*

US Con-
sumption
as % of
World
Total'

US (58)
USSR (20)

US (64)
Canada (14)

T TO

Uo \£j )

USSR (13)

USSR (18)

Cuba (25)
JNew Caledonia
USSR (14)
Canada (14)

Canada (42)

INew Caledonia yZo)

USSR (16)

Saudi Arabia (17)
Kuwait (15)

US (23)
USSR (16)

US (33)
USSR (12)
Japan (6)

Rep. of S. Africa (47) USSR (59)
USSR (47)

Communist

Countries (36)
US (24)

Canada (20)
Mexico (17)
Peru (16)

US (26)

W. Germany (11) 26

Thailand (33)
Malaysia (14)

Malaysia (41)
Bolivia (16)
Thailand (13)

US (24)
Japan (14)

China (73)

China (25)
USSR (19)
US (14)

US (27)
Canada (20)

Canada (23)
USSR (11)
US (8)

US (26)
Japan (13)
USSR (11)

THE LIMITS TO EXPONENTIAL GROWTH

* source: US Bureau of Mines, Mineral Facts and Problems, 1970 (Washington,
DC: Government Printing Office, 1970).

* The number of years known global reserves will last at current global consump-
tion. Calculated by dividing known reserves (column 2) by the current annual
consumption (US Bureau of Mines, Mineral Facts and Problems, 1970).

*' source: US Bureau of Mines, Mineral Facts and Problems, 1970.

1 The number of years known global reserves will last with consumption growing
exponentially at the average annual rate of growth. Calculated by the formula
exponential index = In ((r» s) -f- 1)
r

where r = average rate of growth from column 4
s — static index from column 3.

* The number of years that five times known global reserves will last with con-
sumption growing exponentially at the average annual rate of growth. Calcu-
lated from the above formula with 5s in place of s.

» source: US Bureau of Mines, Mineral Facts and Problems, 1970.

* source: UN Department of Economic and Social Affairs, Statistical Yearbook
1969 (New York: United Nations, 1970).

* sources: Yearbook, of the American Bureau of Metal Statistics 1970 (York, Pa.:
Maple Press, 1970).

World Petroleum Report (New York: Mona Palmer Publishing, 1968).

UN Economic Commission for Europe, The World Market for Iron Ore (New

York: United Nations, 1968).

US Bureau of Mines, Mineral Facts and Problems, 1970.
1 source: US Bureau of Mines, Mineral Facts and Problems, 1970.
1 Bauxite expressed in aluminum equivalent.

k US Bureau of Mines contingency forecasts, based on assumptions that coal will
be used to synthesize gas and liquid fuels.

' Includes US Bureau of Mines estimates of gold demand for hoarding.
m The platinum group metals are platinum, palladium, iridium, osmium, rhodium,
and ruthenium.

ADDITIONAL SOURCES:

P. T. Flawn, Mineral Resources (Skokie, 111.: Rand McNally, 1966).
Metal Statistics (Somerset, NJ: American Metal Market Company, 1970).
US Bureau of Mines, Commodity Data Summary (Washington, DC: Govern-
ment Printing Office, January 1971).

THE LIMITS TO EXPONENTIAL GROWTH

trates the effect of exponentially increasing consumption of a
given initial amount of a nonrenewable resource. The example
in this case is chromium ore, chosen because it has one of the
longest static reserve indices of all the resources listed in table 4.
We could draw a similar graph for each of the resources listed
in the table. The time scales for the resources would vary, but
the general shape of the curves would be the same.

The world's known reserves of chromium are about 775 mil-
lion metric tons, of which about 1.85 million metric tons are
mined annually at present. 13 Thus, at the current rate of use,
the known reserves would last about 420 years. The dashed
line in figure 11 illustrates the linear depletion of chromium
reserves that would be expected under the assumption of con-
stant use. The actual world consumption of chromium is
increasing, however, at the rate of 2.6 percent annually. 13 The
curved solid lines in figure 11 show how that growth rate, if
it continues, will deplete the resource stock, not in 420 years,
as the linear assumption indicates, but in just 95 years. If we
suppose that reserves yet undiscovered could increase present
known reserves by a factor of five, as shown by the dotted line,
this fivefold increase would extend the lifetime of the reserves
only from 95 to 154 years. Even if it were possible from 1970
onward to recycle 100 percent of the chromium (the horizontal
line) so that none of the initial reserves were lost, the demand
would exceed the supply in 235 years.

Figure 1 1 shows that under conditions of exponential growth
in resource consumption, the static reserve index (420 years for
chromium) is a rather misleading measure of resource avail-
ability. We might define a new index, an "exponential reserve
index," which gives the probable lifetime of each resource,
assuming that the current growth rate in consumption will

THE LIMITS TO EXPONENTIAL GROWTH

Figure 11 CHROMIUM RESERVES

im tons

— *r 1

^ 1970 known reserves

235 years ^

Bserves remaining at
onstant 1970 usage r

— i

i
•

A-

reserv
exponf

ss remaining with\
ntially increasing A
usage rate \

reserves remaining with*
exponentially increasing •
usage rate and 5 times 1

—A —

1
1

/ usage rate
/ (lorrs per year)

1 J

■ X
1 /
1 s
1

95 years

^ 00 ^ \ ^ 154 y

jars

1970 2000 2050 2100 2150 2200

The lifetime of known chromium reserves depends on the future usage
rate of chromium. If usage remains constant, reserves will be depleted
linearly (dashed line) and will last 420 years. If usage increases exponen-
tially at its present growth rate of 2.6 percent per year, reserves will be
depleted in just 95 years. If actual reserves are five times present proven
reserves, chromium ore will be available for 154 years (dotted line), assum-
ing exponential growth in usage. Even if all chromium is perfectly recycled,
starting in 1970, exponentially growing demand will exceed the supply
after 235 years (horizontal line).

continue. We have included this index in column 5 of table 4.
We have also calculated an exponential index on the assump-
tion that our present known reserves of each resource can be
expanded fivefold by new discoveries. This index is shown in
column 6. The effect of exponential growth is to reduce the
probable period of availability of aluminum, for example, from
100 years to 31 years (55 years with a fivefold increase in
reserves). Copper, with a 36-year lifetime at the present usage

THE LIMITS TO EXPONENTIAL GROWTH

rate, would actually last only 21 years at the present rate of
growth, and 48 years if reserves are multiplied by five. It is
clear that the present exponentially growing usage rates greatly
diminish the length of time that wide-scale economic growth
can be based on these raw materials.

Of course the actual nonrenewable resource availability in
the next few decades will be determined by factors much more
complicated than can be expressed by either the simple static
reserve index or the exponential reserve index. We have studied
this problem with a detailed model that takes into account
the many interrelationships among such factors as varying
grades of ore, production costs, new mining technology, the
elasticity of consumer demand, and substitution of other re-
sources.* Illustrations of the general conclusions of this model
follow.

Figure 12 is a computer plot indicating the future avail-
ability of a resource with a 400-year static reserve index in
the year 1970, such as chromium. The horizontal axis is time
in years; the vertical axis indicates several quantities, including
the amount of reserves remaining (labeled reserves), the
amount used each year (usage rate), the extraction cost per
unit of resource (actual cost), the advance of mining and
processing technology (indicated by a t), and the fraction of
original use of the resource that has been shifted to a substitute
resource (f).

At first the annual consumption of chromium grows expo-
nentially, and the stock of the resource is rapidly depleted.
The price of chromium remains low and constant because new
developments in mining technology allow efficient use of lower

* A more complete description of this model is presented in the papers
by William W. Behrens III listed in the appendix.

THE LIMITS TO EXPONENTIAL GROWTH

Figure 12 CHROMIUM AVAILABILITY

o u.

This figure presents a computer calculation of the economic factors in the
availability of a resource (chromium) with a 400-year static reserve index.
Exponential growth in consumption is eventually stopped by rising costs as
initial reserves are depleted, even though the technology of extraction and
processing is also increasing exponentially. The usage rate falls to zero
after 125 years, at which point 60 percent of the original uses have been
substituted by another resource.

SOURCE: William W. Behrens III. "The Dynamics of Natural Resource Utilization." Paper
presented at the 1971 Computer Simulation Conference. Boston, Massachusetts. July 1971.

and lower grades of ore. As demand continues to increase,
however, the advance of technology is not fast enough to
counteract the rising costs of discovery, extraction, processing,

THE LIMITS TO EXPONENTIAL GROWTH

Figure 13 CHROMIUM AVAILABILITY WITH
DOUBLE THE KNOWN RESERVES

H a discovery in 1970 doubles the known reserves of the resource (static
reserve index 800 years), exponential growth in the usage rate is prolonged,
and the usage rate reaches a high value. Reserves are depleted very
rapidly during the peak in usage rate, however. Because of this rapid
depletion, the effect of doubling the reserves is not to double the resource
lifetime, but merely to extend it from 125 to 145 years.
SOURCE: William W. Behrens. III. "The Dynamics of Natural Resource Utilization."

and distribution. Price begins to rise, slowly at first and then
very rapidly. The higher price causes consumers to use chro-
mium more efficiently and to substitute other metals for
chromium whenever possible. After 125 years, the remaining
chromium, about 5 percent of the original supply, is available

THE LIMITS TO EXPONENTIAL GROWTH

only at prohibitively high cost, and mining of new supplies
has fallen essentially to zero.

This more realistic dynamic assumption about the future
use of chromium yields a probable lifetime of 125 years, which
is considerably shorter than the lifetime calculated from the
static assumption (400 years), but longer than the lifetime
calculated from the assumption of constant exponential growth
(95 years). The usage rate in the dynamic model is neither
constant nor continuously increasing, but bell-shaped, with a
growth phase and a phase of decline.

The computer run shown in figure 13 illustrates the effect
of a discovery in 1970 that doubles the remaining known
chromium reserves. The static reserve index in 1970 becomes
800 years instead of 400. As a result of this discovery, costs
remain low somewhat longer, so that exponential growth can
continue longer than it did in figure 12. The period during
which use of the resource is economically feasible is increased
from 125 years to 145 years. In other words, a doubling of the
reserves increases the actual period of use by only 20 years.

The earth's crust contains vast amounts of those raw mate-
rials which man has learned to mine and to transform into
useful things. However vast those amounts may be, they are
not infinite. Now that we have seen how suddenly an expo-
nentially growing quantity approaches a fixed upper limit,
the following statement should not come as a surprise. Given
present resource consumption rates and the projected increase
in these rates, the great majority of the currently important
nonrenewable resources will be extremely costly wo years from
now. The above statement remains true regardless of the most
optimistic assumptions about undiscovered reserves, techno-
logical advances, substitution, or recycling, as long as the

THE LIMITS TO EXPONENTIAL GROWTH

demand for resources continues to grow exponentially. The
prices of those resources with the shortest static reserve indices
have already begun to increase. The price of mercury, for
example, has gone up 500 percent in the last 20 years; the
price of lead has increased 300 percent in the last 30 years. 14
The simple conclusions we have drawn by considering total
world reserves of resources are further complicated by the
fact that neither resource reserves nor resource consumption
are distributed evenly about the globe. The last four columns
of table 4 show clearly that the industrialized, consum-
ing countries are heavily dependent on a network of interna-
tional agreements with the producing countries for the supply
of raw materials essential to their industrial base. Added to
the difficult economic question of the fate of various industries
as resource after resource becomes prohibitively expensive is
the imponderable political question of the relationships be-
tween producer and consumer nations as the remaining
resources become concentrated in more limited geographical
areas. Recent nationalization of South American mines and
successful Middle Eastern pressures to raise oil prices suggest
that the political question may arise long before the ultimate
economic one.

Are there enough resources to allow the economic develop-
ment of the 7 billion people expected by the year 2000 to a
reasonably high standard of living? Once again the answer
must be a conditional one. It depends on how the major
resource-consuming societies handle some important decisions
ahead. They might continue to increase resource consumption
according to the present pattern. They might learn to reclaim
and recycle discarded materials. They might develop new
designs to increase the durability of products made from scarce

THE LIMITS TO EXPONENTIAL GROWTH

resources. They might encourage social and economic patterns
that would satisfy the needs of a person while minimizing,
rather than maximizing, the irreplaceable substances he pos-
sesses and disperses.

All of these possible courses involve trade-offs. The trade-
offs are particularly difficult in this case because they involve
choosing between present benefits and future benefits. In order
to guarantee the availability of adequate resources in the future,
policies must be adopted that will decrease resource use in the
present. Most of these policies operate by raising resource costs.
Recycling and better product design are expensive; in most
parts of the world today they are considered "uneconomic."
Even if they were effectively instituted, however, as long as the
driving feedback loops of population and industrial growth
continue to generate more people and a higher resource
demand per capita, the system is being pushed toward its
limit — the depletion of the earth's nonrenewable resources.

What happens to the metals and fuels extracted from the
earth after they have been used and discarded? In one sense
they are never lost. Their constituent atoms are rearranged and
eventually dispersed in a diluted and unusable form into
the air, the soil, and the waters of our planet. The natural
ecological systems can absorb many of the effluents of human
activity and reprocess them into substances that are usable by,
or at least harmless to, other forms of life. When any effluent
is released on a large enough scale, however, the natural absorp-
tive mechanisms can become saturated. The wastes of human
civilization can build up in the environment until they become
visible, annoying, and even harmful. Mercury in ocean fish,
lead particles in city air, mountains of urban trash, oil slicks
on beaches — these are the results of the increasing flow of

THE LIMITS TO EXPONENTIAL GROWTH

resources into and out of man's hands. It is little wonder,
then, that another exponentially increasing quantity in the
world system is pollution.

POLLUTION

Many people . . . are concluding on the basis of mounting and reason-
ably objective evidence that the length of life of the biosphere as an
inhabitable region for organisms is to be measured in decades rather
than in hundreds of millions of years. This is entirely the fault of our
own species. 16

Man's concern for the effect of his activities on the natural
environment is only very recent. Scientific attempts to measure
this effect are even more recent and still very incomplete. We
are certainly not able, at this time, to come to any final con-
clusion about the earth's capacity to absorb pollution. We can,
however, make four basic points in this section, which illus-
trate, from a dynamic, global perspective, how difficult it will
be to understand and control the future state of our ecological
systems. These points are:

1. The few kinds of pollution that actually have been mea-
sured over time seem to be increasing exponentially.

2. We have almost no knowledge about where the upper limits
to these pollution growth curves might be.

3. The presence of natural delays in ecological processes in-
creases the probability of underestimating the control measures
necessary, and therefore of inadvertently reaching those upper
limits.

4. Many pollutants are globally distributed; their harmful
effects appear long distances from their points of generation.

It is not possible to illustrate each of these four points for
each type of pollutant, both because of the space limitations

THE LIMITS TO EXPONENTIAL GROWTH

Figure 14 ENERGY CONSUMPTION AND GNP PER CAPITA

kilograms per person per year (coal equivalent)

US|

' /

-y

Canada
•

— 7

•

i •—

* Sweden
/ •

•

►

•

• ;

I Switzerland

1000

GNP per capita 1000 2000 3000 4000

(1968 US dollars per person per year)

Although the nations of the world consume greatly varying amounts of
energy per capita, energy consumption correlates fairly well with total
output per capita (GNP per capita). The relationship is generally linear,
with the scattering of points due to differences in climate, local fuel prices,
and emphasis on heavy industry.

SOURCES: Energy consumption from UN Department of Economic and Social Affairs,
Statistical Yearbook 1969 (New York: United Nations. 1970). GNP per capita from World
Bank Atlas (Washington, DC: International Bank for Reconstruction and Development,
1970).

THE LIMITS TO EXPONENTIAL GROWTH

of this book and because of the limitations of available data.
Therefore we shall discuss each point using as examples those
pollutants which have been most completely studied to date.
It is not necessarily true that the pollutants mentioned here
are the ones of greatest concern (although they are all of some
concern). They are, rather, the ones we understand best.

Exponentially increasing pollution

Virtually every pollutant that has been measured as a function
of time appears to be increasing exponentially. The rates of
increase of the various examples shown below vary greatly,
but most are growing faster than the population. Some pol-
lutants are obviously directly related to population growth
(or agricultural activity, which is related to population
growth). Others are more closely related to the growth of
industry and advances in technology. Most pollutants in the
complicated world system are influenced in some way by both
the population and the industrialization positive feedback
loops.

Let us begin by looking at the pollutants related to mankind's
increasing use of energy. The process of economic development
is in effect the process of utilizing more energy to increase the
productivity and efficiency of human labor, In fact, one of the
best indications of the wealth of a human population is the
amount of energy it consumes per person (see figure 14). Per
capita energy consumption in the world is increasing at a rate
of 13 percent per year, 16 which means a total increase, includ-
ing population growth, of 3.4 percent per year.

At present about 97 percent of mankind's industrial energy
production comes from fossil fuels (coal, oil, and natural
gas). 17 When these fuels are burned, they release, among other

THE LIMITS TO EXPONENTIAL GROWTH

Figure 15 CARBON DIOXIDE CONCENTRATION
IN THE ATMOSPHERE

parts per million by volume

1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Atmospheric concentration of CO,, observed since 1958 at Mauna Loa,
Hawaii, has increased steadily. At present the increase averages about
1.5 part per million (ppm) each year. Calculations including the known
exchanges of CO, between atmosphere, biosphere, and oceans predict that

THE LIMITS TO EXPONENTIAL GROWTH

the CO, concentration will reach 380 ppm by the year 2000, an increase ot
nearly 30 percent ot the probable value in 1860. The source ot this ex-
ponential increase in atmospheric CO, is man's increasing combustion ot
fossil fuels.

SOURCE: Lester Machta. "The Role ol the Oceens and Biosphere In the Carbon Dioxide
Cycle." Paper presented at Nobel Symposium 20 "The Changing Chemistry ol the
Oceans," Goteborg, Sweden, August 1971.

substances, carbon dioxide (C0 2 ) into the atmosphere. Cur-
rently about 20 billion tons of C0 2 are being released from
fossil fuel combustion each year. 18 As figure 15 shows, the mea-
sured amount of C0 2 in the atmosphere is increasing exponen-
tially, apparently at a rate of about 0.2 percent per year. Only
about one half of the C0 2 released from burning fossil fuels
has actually appeared in the atmosphere — the other half has
apparently been absorbed, mainly by the surface water of the
oceans. 19

If man's energy needs are someday supplied by nuclear
power instead of fossil fuels, this increase in atmospheric CO,
will eventually cease, one hopes before it has had any measur-
able ecological or climatological effect.

There is, however, another side-effect of energy use, which
is independent of the fuel source. By the laws of thermo-
dynamics, essentially all of the energy used by man must
ultimately be dissipated as heat. If the energy source is some-
thing other than incident solar energy (e.g., fossil fuels or
atomic energy), that heat will result in warming the atmos-
phere, either directly, or indirectly through radiation from
water used for cooling purposes. Locally, waste heat or "ther-
mal pollution" in streams causes disruption in the balance of
aquatic life. 20 Atmospheric waste heat around cities causes
the formation of urban "heat islands," within which many
meteorological anomalies occur. 21 Thermal pollution may have
serious climatic effects, worldwide, when it reaches some appre-

THE LIMITS TO EXPONENTIAL GROWTH

Figure 16 WASTE HEAT GENERATION IN THE
LOS ANGELES BASIN

Waste heat released over the 4,000 square mile area of the Los Angeles
basin currently amounts to about 5 percent ot the total solar energy ab-
sorbed at the ground. At the present rate ot growth, thermal release will
reach 18 percent ot incoming solar energy by the year 2000. This heat, the
result of all energy generation and consumption processes, is already
affecting the local climate.

SOURCE: L. Lees in Man's Impact on the Global Environment, Report of the Study of
Critical Environmental Problems (Cambridge, Mass.: MIT Press. 1970).

ciable fraction of the energy normally absorbed by the earth
from the sun. 22 In figure 16, the level of thermal pollution
projected for one large city is shown as a fraction of incident
solar energy.

Nuclear power will produce yet another kind of pollutant
— radioactive wastes. Since nuclear power now provides only
an insignificant fraction of the energy used by man, the pos-
sible environmental impact of the wastes released by nuclear
reactors can only be surmised. Some idea may be gained, how-
ever, by the actual and expected releases of radioactive isotopes
from the nuclear power plants being built today. A partial
list of the expected annual discharge to the environment of a

THE LIMITS TO EXPONENTIAL GROWTH

Figure 17 NUCLEAR WASTES

billion million

thousands ol megawatts Curies Curies

1970 1980 1990 2000

Installed nuclear generating capacity in the United States is expected to
grow from 11 thousand megawatts In 1970 to more than 900 thousand
megawatts in the year 2000. Total amount of stored nuclear wastes, radio-
active by-products of the energy production, will probably exceed one
thousand billion Curies by that year. Annual release of nuclear wastes,
mostly in the form of krypton gas and tritium in cooling water, will reach
25 million Curies, if present release standards are still in effect.

SOURCES: Installed capacity to 1985 from US Atomic Energy Commission, Forecast ot
Growth ol Nuclear Power (Washington, DC: Government Printing Office, 1971). Installed
capacity to 2000 from Chauncey Starr, "Energy and Power," Scientific American, Sep-
tember 1971. Stored nuclear wastes from J. A. Snow, "Radioactive Waste from Reactors,"
Scientist and Citizen 9 (1967). Annual release of nuclear wastes calculated from specifica-
tions for 1.6 thousand megawatt plant In Calvert Cliffs, Maryland.

1.6 million kilowatt plant now under construction in the
United States includes 42,800 Curies * of radioactive krypton

* A Curie is the radioactive equivalent of one gram of radium. This is
such a large amount of radiation that environmental concentrations are
usually expressed in microcuries (millionths of a Curie).

THE LIMITS TO EXPONENTIAL GROWTH

Figure 18 CHANGES IN CHEMICAL CHARACTERISTICS AND
COMMERCIAL FISH PRODUCTION IN LAKE ONTARIO

parts per million

•

total
•

dissolve

d solids

•

180

160

1(50 1860 1170 1X80 1

ln parts per million

690 1900 1910 1920 1930 1940 1950 1960 1970

•

15.

•

calci

im — ^

•

-J^

r o

sulfa

--42

I-

chlori

de-v

■-.

sodiurr

& pota:

sium s

1870 1880 1890 1900 1910 1920 1930 1940 1950 1960

As a result of heavy dumping of municipal, industrial, and agricultural
wastes into Lake Ontario, the concentrations of numerous salts have been
rising exponentially. The chemical changes in the lake have resulted in
severe declines in the catches of most commercially valuable fish. It should
be noted that the plotting scale for fish catch is logarithmic, and thus the
fish catch has decreased by factors of 100 to 1,000 for I

THE LIMITS TO EXPONENTIAL GROWTH

millions of pounds per year millions ol pounds per year

lake herring and chubs 1 n blue pike

10-s I I I I I I I I I I I I I I I
1900 1910 1920 1930 1940 1950 19(0 1970

SOURCE: A. M. Beeton. Statement on Pollution and Eutrophication ol the Great Lakes,
The University of Wisconsin Center for Great Lakes Studies Special Report #11 (Milwau-
kee, Wise: University of Wisconsin, 1970).

THE LIMITS TO EXPONENTIAL GROWTH

Figure 19 OXYGEN CONTENT OF THE BALTIC SEA

percent of saturation

• <

•

•
•

•

— •—

•
•

•

1900 1910 1920 1930,1940 1950 1960 1970'

Increasing accumulation of organic wastes in the Baltic Sea, where water
circulation is minimal, has resulted in a steadily decreasing oxygen con-
centration in the water. In some areas, especially in deeper waters, oxygen
concentration is zero and almost no forms of aquatic lite can be supported.

SOURCE: Stig H. Fonselius, "Stagnant Sea." Environment, July/August 1970.

(half-life ranging from a few hours to 9.4 years, depending on
the isotope) in the stack gases, and 2,910 Curies of tritium
(half-life 12.5 years) in the waste water. 23 Figure 17 shows
how the nuclear generating capacity of the United States is
expected to grow from now until the year 2000. The graph
also includes an estimate of radioactive wastes annually re-
leased by these nuclear power plants and of accumulated
wastes (from spent reactor fuels) that will have to be safely
stored.

Carbon dioxide, thermal energy, and radioactive wastes are
just three of the many disturbances man is inserting into the
environment at an exponentially increasing rate. Other ex-
amples are shown in figures 18-21.

Figure 18 shows the chemical changes occurring in a large
North American lake from accumulation of soluble industrial,

THE LIMITS TO EXPONENTIAL GROWTH

Figure 20 US MERCURY CONSUMPTION

thousands ol 76 lb. flasks

total consumption

consumption tor caustic soda and
chlorine production

1946 48 50 52.54 56 5 8 60 62 64 66 68

Mercury consumption in the United States shows an exponential trend, on
which short-term market fluctuations are superimposed. A large part of the
mercury is used for the production of caustic soda and chlorine. The chart
does not include the rising amount of mercury released into the atmosphere
from the combustion of fossil fuels.

SOURCE: Barry Commoner, Michael Carr, and Paul J. Stamler, "The Causes of Pollution,"
Environment, April 1971.

agricultural, and municipal wastes. The accompanying de-
crease in commercial fish production from the lake is also
indicated. Figure 19 illustrates why the increase in organic
wastes has such a catastrophic effect on fish life. The figure
shows the amount of dissolved oxygen (which fish "breathe")
in the Baltic Sea as a function of time. As increasing amounts
of wastes enter the water and decay, the dissolved oxygen is
depleted. In the case of some parts of the Baltic, the oxygen
level has actually reached zero.

The toxic metals lead and mercury are released into water-
ways and into the atmosphere from automobiles, incinerators,

THE LIMITS TO EXPONENTIAL GROWTH

Figure 21 LEAD IN THE GREENLAND ICE CAP

micrograms

wleadllon ol snow
-sea salt/kilogram ol snow
--•calcium/kilogram ol snow

1750 1800 1850

age of snow strata

1900

1950

Deep samples of snow from the Greenland Ice Sheet show Increasingly high
deposits of lead over time. Concentrations of calcium and sea salt were
also measured as a control. Presence of lead reflects Increasing world
industrial use of the metal, including direct release into the atmosphere
from automobile exhausts.

SOURCE: C. C. Patterson and J. O. Salvia, "Lead In the Modern Environment— How Much
Is Natural?" Scientist and Citizen, April 1960.

industrial processes, and agricultural pesticides. Figure 20
shows the exponential increase in mercury consumption in
the United States from 1946 to 1968. Only 18 percent of this
mercury is captured and recycled after use. 24 An exponential
increase in deposits of airborne lead has been detected by
extraction of successively deeper samples from the Greenland
ice cap, as shown in figure 21.

Unknown upper limits

All of these exponential curves of various kinds of pollution can
be extrapolated into the future, as we have extrapolated land
needs in figure 10 and resource use in figure 11. In both of

THE LIMITS TO EXPONENTIAL GROWTH

these previous figures, the exponential growth curve eventually
reached an upper limit — the total amount of arable land or
of resources economically available in the earth. However, no
upper bounds have been indicated for the exponential growth
curves of pollutants in figures 15-21, because it is not known
how much we can perturb the natural ecological balance of
the earth without serious consequences. It is not known how
much C0 2 or thermal pollution can be released without caus-
ing irreversible changes in the earth's climate, or how much
radioactivity, lead, mercury, or pesticide can be absorbed by
plants, fish, or human beings before the vital processes are
severely interrupted.

Natural delays in ecological processes

This ignorance about the limits of the earth's ability to absorb
pollutants should be reason enough for caution in the release
of polluting substances. The danger of reaching those limits
is especially great because there is typically a long delay be-
tween the release of a pollutant into the environment and the
appearance of its negative effect on the ecosystem. The
dynamic implications of such a delayed effect can be illustrated
by the path of DDT through the environment after its use as
an insecticide. The results presented below are taken from a
detailed System Dynamics study* using the numerical con-
stants appropriate to DDT. The general conclusion is appli-
cable (with some change in the exact numbers involved) to
all long-lived toxic substances, such as mercury, lead, cadmium,
other pesticides, polychlorobiphenyl (PCB), and radioactive
wastes.

* The study, by Jtf rgen Randers and Dennis L. Meadows, is listed in the
appendix.

THE LIMITS TO EXPONENTIAL GROWTH

DDT is a man-made organic chemical released into the
environment as a pesticide at a rate of about 100,000 tons
annually. 26 After its application by spraying, part of it evap-
orates and is carried long distances in the air before it eventu-
ally precipitates back onto the land or into the ocean. In the
ocean some of the DDT is taken up by plankton, some of the
plankton are eaten by fish, and some of the fish are finally
eaten by man. At each step in the process the DDT may be
degraded into harmless substances, it may be released back
into the ocean, or it may be concentrated in the tissues of
living organisms. There is some time delay involved at each
of these steps. All these possible pathways have been analyzed
by a computer to produce the results seen in figure 22.

The DDT application rate shown in the figure follows the
world application rate from 1940 to 1970. The graph shows
what would happen if in 1970 the world DDT application
rate began to decrease gradually until it reached zero in the
year 2000. Because of the inherent delays in the system, the
level of DDT in fish continues to rise for more than 10 years
after DDT use starts declining, and the level in fish does not
come bac\ down to the igjo level until the year /095 — more
than two decades after the decision is made to reduce DDT
application.

Whenever there is a long delay from the time of release of a
pollutant to the time of its appearance in a harmful form,
we know there will be an equally long delay from the time
of control of that pollutant to the time when its harmful effect
finally decreases. In other words, any pollution control system
based on instituting controls only when some harm is already
detected will probably guarantee that the problem will get
much worse before it gets better. Systems of this sort are

THE LIMITS TO EXPONENTIAL GROWTH

Figure 22 DDT FLOWS IN THE ENVIRONMENT

fr 11 years-)
i

1
V

\ i
\ i

DDT in fish

_v____.

DDT In soil ■

application

rate ^%

Calculation ot the path ot DDT through the environment shows the prob-
able result If the world DDT application rate began to decline In 1970. The
application rate shown is historically correct to 1970. DDT in soil peaks
shortly after the application rate begins to decline, but DDT in fish con-
tinues to rise for 11 years and does not tall back to its 1970 level until 1995.
DDT in fish-eating animals, such as birds and man, would show an even
longer delay in responding to the decrease in application rate.

md Dennis L. Meadows. "System Simulation to Test Environ-
I: A Sample Study ot DDT Movement in the Environment" (Cambridge.

ry, 1»71).

THE LIMITS TO EXPONENTIAL GROWTH

exceedingly difficult to control, because they require that
present actions be based on results expected far in the future.

Global distribution of pollutants

At the present time only the developed nations of the world
are seriously concerned about pollution. It is an unfortunate
characteristic of many types of pollution, however, that even-
tually they become widely distributed around the world.
Although Greenland is far removed from any source of atmo-
spheric lead pollution, the amount of lead deposited in Green-
land ice has increased 300 percent yearly since 1940. 28 DDT has
accumulated in the body fat of humans in every part of the
globe, from Alaskan eskimos to city-dwellers of New Delhi, as
shown in table 5.

Pollution Limits

Since pollution generation is a complicated function of popu-
lation, industrialization, and specific technological develop-
ments, it is difficult to estimate exactly how fast the exponen-
tial curve of total pollution release is rising. We might estimate
that if the 7 billion people of the year 2000 have a GNP per
capita as high as that of present-day Americans, the total
pollution load on the environment would be at least ten times
its present value. Can the earth's natural systems support an
intrusion of that magnitude? We have no idea. Some people
believe that man has already so degraded the environment that
irreversible damage has been done to large natural systems.
We do not know the precise upper limit of the earth's ability
to absorb any single kind of pollution, much less its ability
to absorb the combination of all kinds of pollution. We do
know however that there is an upper limit. It has already been
surpassed in many local environments. The surest way to

THE LIMITS TO EXPONENTIAL GROWTH

Table 5 DDT IN BODY FAT Concentration

of DDT and
toxic breakdown
products in

Population

Year

Number in
sample

body fat
( parts per million)

Alaska (Eskimos)

1960

3.0

Canada

1959-60

4.9

England

1961-62

131

2.2

England

1964

100

3.9

France ._

1961

D.Z

Germany

1958-59

2.3

Hungary

1960

12.4

India (Delhi)

1964

26.0

Israel

1963-64

254

19.2

United States (Kentucky)

1942

United States

(Georgia, Kentucky,

Arizona, Washington) ....

1961-62

130

12.7

United States (all areas) ....

1964

7.6

source: Wayland J. Hayes, Jr., "Monitoring Food and People for Pesticide Content,"
in Scientific Aspects of Pest Control (Washington, DC: National Academy of Sci-
ences — National Research Council, 1966).

reach that upper limit globally is to increase exponentially
both the number of people and the polluting activities of each
person.

The trade-offs involved in the environmental sector of the
world system are every bit as difficult to resolve as those in
the agricultural and natural resource sectors. The benefits of
pollution-generating activities are usually far removed in both
space and time from the costs. To make equitable decisions,
therefore, one must consider both space and time factors. If
wastes are dumped upstream, who will suffer downstream? If
fungicides containing mercury are used now, to what extent,

THE LIMITS TO EXPONENTIAL GROWTH

when, and where will the mercury appear in ocean fish? If
polluting factories are located in remote areas to "isolate" the
pollutants, where will those pollutants be ten or twenty years
from now ?

It may be that technological developments will allow the
expansion of industry with decreasing pollution, but only at a
high cost. The US Council on Environmental Quality has
called for an expenditure of $105 billion between now and
1975 (42 percent of which is to be paid by industry) for just a
partial cleanup of American air, water, and solid-waste pollu-
tion. 27 Any country can postpone the payment of such costs
to increase the present growth rate of its capital plant, but
only at the expense of future environmental degradation,
which may be reversible only at very high cost.

A FINITE WORLD

We have mentioned many difficult trade-offs in this chapter
in the production of food, in the consumption of resources,
and in the generation and clean-up of pollution. By now it
should be clear that all of these trade-offs arise from one simple
fact — the earth is finite. The closer any human activity comes
to the limit of the earth's ability to support that activity, the
more apparent and unresolvable the trade-offs become. When
there is plenty of unused arable land, there can be more people
and aho more food per person. When all the land is already
used, the trade-off between more people or more food per
person becomes a choice between absolutes.

In general, modern society has not learned to recognize and
deal with these trade-offs. The apparent goal of the present
world system is to produce more people with more (food,
material goods, clean air and water) for each person. In this

THE LIMITS TO EXPONENTIAL GROWTH

chapter we have noted that if society continues to strive for
that goal, it will eventually reach one of many earthly limita-
tions. As we shall see in the next chapter, it is not possible
to foretell exactly which limitation will occur first or what
the consequences will be, because there are many conceivable,
unpredictable human responses to such a situation. It is
possible, however, to investigate what conditions and what
changes in the world system might lead society to collision
with or accommodation to the limits to growth in a finite
world.

CHAPTER III

GROWTH
IN

THE

WORLD

SYSTEM

In the circumference of a circle the
beginning and end are common.

HERACUTUS, 500 B.C.

We have discussed food, nonrenew-
able resources, and pollution absorption as separate factors
necessary for the growth and maintenance of population and
industry. We have looked at the rate of growth in the demand
for each of these factors and at the possible upper limits to the
supply. By making simple extrapolations of the demand
growth curves, we have attempted to estimate, roughly, how
much longer growth of each of these factors might continue
at its present rate of increase. Our conclusion from these
extrapolations is one that many perceptive people have already
realized — that the short doubling times of many of man's
activities, combined with the immense quantities being
doubled, will bring us close to the limits to growth of those
activities surprisingly soon.

Extrapolation of present trends is a time-honored way of
looking into the future, especially the very near future, and
especially if the quantity being considered is not much in-

GROWTH IN THE WORLD SYSTEM

flucnced by other trends that arc occurring elsewhere in the
system. Of course, none of the five factors we are examining
here is independent. Each interacts constantly with all the
others. We have already mentioned some of these interactions.
Population cannot grow without food, food production is
increased by growth of capital, more capital requires more
resources, discarded resources become pollution, pollution inter-
feres with the growth of both population and food.

Furthermore, over long time periods each of these factors
also feeds back to influence itself. The rate at which food pro-
duction increases in the 1970's, for example, will have some
effect on the size of the population in the 1980's, which will in
turn determine the rate at which food production must increase
for many years thereafter. Similarly, the rate of resource
consumption in the next few years will influence both the size
of the capital base that must be maintained and the amount
of resources left in the earth. Existing capital and available
resources will then interact to determine future resource supply
and demand.

The five basic quantities, or levels — population, capital, food,
nonrenewable resources, and pollution — are joined by still other
interrelationships and feedback loops that we have not yet dis-
cussed. Clearly it is not possible to assess the long-term future of
any of these levels without taking all the others into account.
Yet even this relatively simple system has such a complicated
structure that one cannot intuitively understand how it will
behave in the future, or how a change in one variable might
ultimately affect each of the others. To achieve such under-
standing, we must extend our intuitive capabilities so that we
can follow the complex, interrelated behavior of many variables
simultaneously.

GROWTH IN THE WORLD SYSTEM

In this chapter we describe the formal world model that
we have used as a first step toward comprehending this com-
plex world system. The model is simply an attempt to bring
together the large body of knowledge that already exists about
cause-and-effect relationships among the five levels listed above
and to express that knowledge in terms of interlocking feed-
back loops. Since the world model is so important in under-
standing the causes of and limits to growth in the world sys-
tem, we shall explain the model-building process in some
detail.

In constructing the model, we followed four main steps:

1. We first listed the important causal relationships among the
five levels and traced the feedback loop structure. To do so
we consulted literature and professionals in many fields of
study dealing with the areas of concern — demography, eco-
nomics, agronomy, nutrition, geology, and ecology, for ex-
ample. Our goal in this first step was to find the most basic
structure that would reflect the major interactions between the
five levels. We reasoned that elaborations on this basic struc-
ture, reflecting more detailed knowledge, could be added after
the simple system was understood.

2. We then quantified each relationship as accurately as
possible, using global data where it was available and char-
acteristic local data where global measurements had not been
made.

3. With the computer, we calculated the simultaneous opera-
tion of all these relationships over time. We then tested the
effect of numerical changes in the basic assumptions to find
the most critical determinants of the system's behavior.

4. Finally, we tested the effect on our global system of the

GROWTH IN THE WORLD SYSTEM

various policies that are currently being proposed to enhance
or change the behavior of the system.

These steps were not necessarily followed serially, because
often new information coming from a later step would lead
us back to alter the basic feedback loop structure. There is not
one inflexible world model ; there is instead an evolving model
that is continuously criticized and updated as our own under-
standing increases.

A summary of the present model, its purpose and limita-
tions, the most important feedback loops it contains, and our
general procedure for quantifying causal relationships follows.

THE PURPOSE OF THE WORLD MODEL

In this first simple world model, we are interested only in
the broad behavior modes of the population-capital system.
By behavior modes we mean the tendencies of the variables
in the system (population or pollution, for example) to change
as time progresses. A variable may increase, decrease, remain
constant, oscillate, or combine several of these characteristic
modes. For example, a population growing in a limited envi-
ronment can approach the ultimate carrying capacity of that
environment in several possible ways. It can adjust smoothly
to an equilibrium below the environmental limit by means of
a gradual decrease in growth rate, as shown below. It can over-

GROWTH IN THE WORLD SYSTEM

shoot the limit and then die back again in either a smooth or
an oscillatory way, also as shown below. Or it can overshoot

.-carrying capacity

*7\

^ carrying capacity

/ ^— population

time

the limit and in the process decrease the ultimate carrying
capacity by consuming some necessary nonrenewable resource,
as diagramed below. This behavior has been noted in many
natural systems. For instance, deer or goats, when natural
enemies are absent, often overgraze their range and cause
erosion or destruction of the vegetation. 28

carrying capacity

A major purpose in constructing the world model has been
to determine which, if any, of these behavior modes will be
most characteristic of the world system as it reaches the limits
to growth. This process of determining behavior modes is
"prediction" only in the most limited sense of the word. The
output graphs reproduced later in this book show values for

GROWTH IN THE WORLD SYSTEM

world population, capital, and other variables on a time scale
that begins in the year 1900 and continues until 2100. These
graphs are not exact predictions of the values of the variables
at any particular year in the future. They are indications of
the system's behavioral tendencies only.

The difference between the various degrees of "prediction"
might be best illustrated by a simple example. If you throw a
ball straight up into the air, you can predict with certainty
what its general behavior will be. It will rise with decreasing
velocity, then reverse direction and fall down with increasing
velocity until it hits the ground. You know that it will not
continue rising forever, rior begin to orbit the earth, nor loop
three times before landing. It is this sort of elemental under-
standing of behavior modes that we are seeking with the
present world model. If one wanted to predict exactly how
high a thrown ball would rise or exactly where and when it
would hit the ground, it would be necessary to make a detailed
calculation based on precise information about the ball, the
altitude, the wind, and the force of the initial throw. Similarly,
if we wanted to predict the size of the earth's population in
1993 within a few percent, we would need a very much more
complicated model than the one described here. We would
also need information about the world system more precise
and comprehensive than is currently available.

Because we are interested at this point only in broad behavior
modes, this first world model need not be extremely detailed.
We thus consider only one general population, a population
that statistically reflects the average characteristics of the global
population. We include only one class of pollutants — the long-
lived, globally distributed family of pollutants, such as lead,
mercury, asbestos, and stable pesticides and radioisotopes—

GROWTH IN THE WORLD SYSTEM

whose dynamic behavior in the ecosystem we. are beginning
to understand. We plot one generalized resource that represents,
the combined reserves of all nonrenewable resources, although
we know that each separate resource will follow the general
dynamic pattern at its own specific level and rate.

This high level of aggregation is necessary at this point to
keep the model understandable. At the same time it limits the
information we can expect to gain from the model. Questions
of detail cannot be answered because the model simply does
not yet contain much detail. National boundaries are not recog-
nized. Distribution inequalities of food, resources, and capital
are included implicitly in the data but they are not calculated
explicitly nor graphed in the output. World trade balances,
migration patterns, climatic determinants, and political proc-
esses are not specifically treated. Other models can, and we
hope will, be built to clarify the behavior of these important
subsystems.*

Can anything be learned from such a highly aggregated
model ? Can its output be considered meaningful ? In terms of
exact predictions, the output is not meaningful. We cannot
forecast the precise population of the United States nor the GNP
of Brazil nor even the total world food production for the year
2015. The data we have to work with are certainly not suffi-
cient for such forecasts, even if it were our purpose to make
them. On the other hand, it is vitally important to gain some
understanding of the causes of growth in human society, the
limits to growth, and the behavior of our socio-economic sys-
tems when the limits are reached. Man's knowledge of the

•We have built numerous submodels ourselves in the course of this
study to investigate the detailed dynamics underlying each sector of
the world model. A list of those studies is included in the appendix.

GROWTH IN THE WORLD SYSTEM

I POPULATION GROWTH AND CAPITAL GROWTH
FEEDBACK LOOPS

population

total number
of people

births per year

fertility

deaths per year-

mortality
( life expectancy)

industrial output

investment

per year)

investment rate

depreciation
( ) (capital becoming obsolete
or worn out per year)

average lifetime
of capital

The central feedback loops of the world model govern the growth of popu-
lation and of industrial capital. The two positive feedback loops involving
births and investment generate the exponential growth behavior of popula-
tion and capital. The two negative feedback loops involving deaths and
depreciation tend to regulate this exponential growth. The relative strengths
of the various loops depend on many other factors in the world system.

behavior modes of these systems is very incomplete. It is cur-
rently not known, for example, whether the human population
will continue growing, or gradually level off, or oscillate

CROWTH IN THE WORLD SYSTEM

around some upper limit, or collapse. We believe that the
aggregated world model is one way to approach such ques-
tions. The model utilizes the most basic relationships among
people, food, investment, depreciation, resources, output —
relationships that are the same the world over, the same in any
part of human society or in society as a whole. In fact, as we
indicated at the beginning of this book, there are advantages
to considering such questions with as broad a space-time hori-
zon as possible. Questions of detail, of individual nations, and
of short-term pressures can be asked much more sensibly when
the overall limits and behavior modes are understood.

THE FEEDBACK LOOP STRUCTURE

In chapter I we drew a schematic representation of the feed-
back loops that generate population growth and capital
growth. They are reproduced together in figure 23.

A review of the relationships diagramed in figure 23 may
be helpful. Each year the population is increased by the total
number of births and decreased by the total number of deaths
that have taken place during that year. The absolute number
of births per year is a function of the average fertility of the
population and of the size of the population. The number of
deaths is related to the average mortality and the total popu-
lation size. As long as births exceed deaths, the population
grows. Similarly, a given amount of industrial capital, operat-
ing at constant efficiency, will be able to produce a certain
amount of output each year. Some of that output will be more
factories, machines, etc., which are investments to increase the
stock of capital goods. At the same time some capital equip-
ment will depreciate or be discarded each year. To keep indus-
trial capital growing, the investment rate must exceed the

GROWTH IN THE WORLD SYSTEM

Figure 24 FEEDBACK LOOPS OF POPULATION, CAPITAL,
AGRICULTURE, AND POLLUTION

population

Some of the interconnections between population and industrial capital
operate through agricultural capital, cultivated land, and pollution. Each
arrow indicates a causal relationship, which may be immediate or delayed,
large or small, positive or negative, depending on the assumptions included
in each model run.

GROWTH IN THE WORLD SYSTEM

depreciation rate.

In all our flow diagrams, such as figure 23, the arrows simply
indicate that one variable has some influence on another. The
nature and degree of influence are not specified, although of
course they must be quantified in the model equations. For
simplicity, we often omit noting in the flow diagrams that
several of the causal interactions occur only after a delay. The
delays are included explicitly in the model calculations.

Population and capital influence each other in many ways,
some of which are shown in figure 24. Some of the output of
industrial capital is agricultural capital — tractors, irrigation
ditches, and fertilizers, for example. The amount of agricul-
tural capital and land area under cultivation strongly influences
the amount of food produced. The food per capita (food pro-
duced divided by the population) influences the mortality of
the population. Both industrial and agricultural activity can
cause pollution. (In the case of agriculture, the pollution con-
sists largely of pesticide residues, fertilizers that cause eutrophi-
cation, and salt deposits from improper irrigation.) Pollution
may affect the mortality of the population directly and also
indirectly by decreasing agricultural output. 2 "

There are several important feedback loops in figure 24. If
everything else in the system remained the same, a population
increase would decrease food per capita, and thus increase mor-
tality, increase the number of deaths, and eventually lead to a
population decrease. This negative feedback loop is diagramed
below.

GROWTH IN THE WORLD SYSTEM

population

deaths per year

(-)

food per capita

mortality

Another negative feedback loop (shown below) tends to
counterbalance the one shown above. If the food per capita
decreases to a value lower than that desired by the population,
there will be a tendency to increase agricultural capital, so
that future food production and food per capita can increase.

food

desired food
per capita

agricultural

Other important relationships in the world model are illus-
trated in figure 25. These relationships deal with population,
industrial capital, service capital, and resources.

Industrial output includes goods that are allocated to service
capital — houses, schools, hospitals, banks, and the equipment
they contain. The output from this service capital divided by
the population gives the average value of services per capita.
Services per capita influence the level of health services and
thus the mortality of the population. Services also include edu-
cation and research into birth control methods as well as
distribution of birth control information and devices. Services
per capita are thus related to fertility.

GROWTH IN THE WORLD SYSTEM

Figure 25 FEEDBACK LOOPS OF POPULATION, CAPITAL, SERVICES,
AND RESOURCES

population

(+)

industrial output
per capita

(+)
education,
family planning

deaths per year

mortality
(-) J

health services

services
per capita

industrial output

investment
investment rate

industrial
capital

(-)

depreciation
\

average lifetime
of capital

Population and industrial capital are also influenced by the levels of service
capital (such as health and education services) and of nonrenewable re-
source reserves.

100

GROWTH IN THE WORLD SYSTEM

A changing industrial output per capita also has an observ-
able effect (though typically after a long delay) on many social
factors that influence fertility.

Each unit of industrial output consumes some nonrenewable
resource reserves. As the reserves gradually diminish, more
capital is necessary to extract the same amount of resource from
the earth, and thus the efficiency of capital decreases (that is,
more capital is required to produce a given amount of finished
goods).

The important feedback loops in figure 25 are shown below.

GROWTH IN THE WORLD SYSTEM

Figure 26 THE WORLD MODEL

The entire world model is represented here by a flow diagram in formal
System Dynamics notation. Levels, or physi cal q uantities that can be meas-
ured directly, are indicated by rectangles rates that influence those
levels by valves and auxiliary variables that influence the rate equa-
tions by circles #. Time delays are indicated by sections within rec-
tangles £25 Real flows of people, goods, money, etc. are shown by solid

arrows ► and causal relationships by broken arrows 1

Clouds represent sources or sinks that are not important to the

model behavior.

The relationships shown in figures 24 and 25 are typical of
the many interlocking feedback loops in the world model.
Other loops include such factors as the area of cultivated land
and the rate at which it is developed or eroded, the rate at
which pollution is generated and rendered harmless by the
environment, and the balance between the labor force and the
number of jobs available. The complete flow diagram for the
world model, incorporating all these factors and more, is shown
in figure 26.

QUANTITATIVE ASSUMPTIONS

Each of the arrows in figure 26 represents a general relation-
ship that we know is important or potentially important in the
population-capital system. The structure is, in fact, sufficiently
general that it might also represent a single nation or even a
single city (with the addition of migration and trade flows
across boundaries). To apply the model structure of figure 26
to a nation, we would quantify each relationship in the struc-
ture with numbers characteristic of that nation. To represent
the world, the data would have to reflect average characteris-
tics of the whole world.
Most of the causal influences in the real world are nonlinear.

104

GROWTH IN THE WORLD SYSTEM

That is, a certain change in a causal variable (such as an
increase of 10 percent in food per capita) may affect another
variable (life expectancy, for example) differently, depending
on the point within the possible range of the second variable
at which the change takes place. For instance, if an increase
in food per capita of 10 percent has been shown to increase
life expectancy by 10 years, it may not follow that an increase
of food per capita by 20 percent will increase life expectancy
by 20 years. Figure 27 shows the nonlinearity of the relation-
ship between food per capita and life expectancy. If there is
little food, a small increase may bring about a large increase
in life expectancy of a population. If there is already sufficient
food, a further increase will have little or no effect. Nonlinear
relationships of this sort have been incorporated directly into
the world model.*

The current state of knowledge about causal relationships in
the world ranges from complete ignorance to extreme accuracy.
The relationships in the world model generally fall in the
middle ground of certainty. We do know something about
the direction and magnitude of the causal effects, but we rarely
have fully accurate information about them. To illustrate how
we operate on this intermediate ground of knowledge, we pre-
sent here three examples of quantitative relationships from the
world model. One is a relationship between economic variables
that is relatively well understood; another involves socio-
psychological variables that are well studied but difficult to
quantify; and the third one relates biological variables that

* The data in figure 27 have not been corrected for variations in other
factors, such as health care. Further information on statistical treatmen'
of such a relationship and on its incorporation into the model equations
will be presented in the technical report.

105

GROWTH IN THE WORLD SYSTEM

Figure 27 NUTRITION AND LIFE EXPECTANCY

years ol lite expectancy tor males

4
*

** •
•

• _

•

• ,

•

•
•

•

t-Jk

/ •

— •-

•/

•

2,000 4,000 6,000 8,000 10,000 12,000

nutritional level (vegetable calorie equivalents)

Lite expectancy of a population is a nonlinear function of (he nutrition that
the population receives. In this graph nutritional level is given in vegetable
calorie equivalents. Calories obtained from animal sources, such as meat
or milk, are multiplied by a conversion factor (roughly 7, since about 7
calories of vegetable feed are required to produce 1 calorie of animal
origin). Since food from animal sources is of greater value in sustaining
human life, this measure takes into account both quantity and quality of
food. Each point on the graph represents the average life expectancy and
nutritional level of one nation in 1953.

SOURCE: M. C4p*de, F. Houtart, and L. Grond, Population and Food (New York: Sheed
and Ward, 1964).

106

GROWTH IN THE WORLD SYSTEM

are, as yet, almost totally unknown. Although these three
examples by no means constitute a complete description of
the world model, they illustrate the reasoning we have used to
construct and quantify it.

Per capita resource use

As the world's population and capital plant grow, what will
happen to the demand for nonrenewable resources? The
amount of resources consumed each year can be found by mul-
tiplying the population times the per capita resource usage rate.
Per capita resource usage rate is not constant, of course. As a
population becomes more wealthy, it tends to consume more
resources per person per year. The flow diagram expressing
the relationship of population, per capita resource usage rate,
and wealth (as measured by industrial output per capita) to
the resource usage rate is shown below.

nonrenewable
resource

The relationship between wealth (industrial output per
capita) and resource demand (per capita resource usage rate)
is expressed by a nonlinear curve of the form shown in figure
28. In figure 28 resource use is defined in terms of the world
average resource consumption per capita in 1970, which is set

107

GROWTH IN THE WORLD SYSTEM

Figure 28 INDUSTRIAL OUTPUT PER CAPITA AND
RESOURCE USAGE

GNP per capita ( US dollars per person per year)

200 500 1000 1500 2000 2500 3000

200 400 600 800 1000 1200 1400 1600

industrial output per capita (L/S dollars per person per year)

The postulated model relationship between resources consumed per person
and industrial output per person is S-shaped. In nonindustrialized societies
resource consumption is very low, since most production is agricultural.
As industrialization increases, nonrenewable resource consumption rises
steeply, and then becomes nearly level at a very high rate ol consumption.
Point x indicates the 1970 world average resource consumption rate;
point + indicates the 1970 US average consumption rate. The two hori-
zontal scales give the resource consumption relationship in terms of both
industrial output per capita and GNP per capita.

equal to 1. Since world average industrial output per capita
in 1970 was about $230, 3 ° we know that the curve goes through
the point marked by an X. In 1970 the United States had an
average industrial output per capita of about $1,600, and the
average citizen consumed approximately seven times the world
average per capita resource usage. 31 The point on the curve that
would represent the US level of consumption is marked by

108

GROWTH IN THE WORLD SYSTEM

a +. We assume that, as the rest of the world develops eco-
nomically, it will follow basically the US pattern of consump-
tion — a sharp upward curve as output per capita grows, fol-
lowed by a leveling off. Justification for that assumption can
be found in the present pattern of world steel consumption
(see figure 29). Although there is some variation in the steel
consumption curve from the general curve of figure 28, the
overall pattern is consistent, even given the differing economic
and political structures represented by the various nations.

Additional evidence for the general shape of the resource
consumption curve is shown by the history of US consumption
of steel and copper plotted in figure 30. As the average indi-
vidual income has grown, the resource usage in both cases has
risen, at first steeply and then less steeply. The final plateau
represents an average saturation level of material possessions.
Further income increases are spent primarily on services, which
are less resource consuming.

The S-shaped curve of resource usage shown in figure 28
is included in the world model only as a representation of
apparent present policies. The curve can be altered at any time
in the model simulation to test the effects of system changes
(such as recycling of resources) that would either increase or
decrease the amount of nonrenewable resources each person
consumes. Actual model runs shown later in this book will
illustrate the effects of such policies.

Desired birth rate

The number of births per year in any population equals the
number of women of reproductive age times the average fer-
tility (the average number of births per woman per year).
There may be numerous factors influencing the fertility of a

109

GROWTH IN THE WORLD SYSTEM

700

Figure 29 WORLD STEEL CONSUMPTION AND GNP PER CAPITA

kilograms per person per year — 1968

00 1000 1500 2000 2500 3000 3500

GNP per capita — 1968 ( US dollars per person per year}

1968 steel consumption per person In various nations ol the world follows
the general S-shaped pattern shown in figure 28.

SOURCES: Steel consumption from UN Department of Economic and Social Affairs,
Statistical Yearbook 1989 (New York: United Nations, 1970). GNP per capita from World
Bank Atlas (Washington, DC: International Bank for Reconstruction and Development,
1970).

population. In fact the study of fertility determinants is a major
occupation of many of the world's demographers. In the world
model we have identified three major components of fertility —
maximum biological birth rate, birth control effectiveness, and
desired birth rate. The relationship of these components to fer-
tility is expressed in the diagram below.

birth rale

110

fertility

birth control
effectiveness

service output

desired
birth rate

industrial output

GROWTH IN THE WORLD SYSTEM

Figure 30 US COPPER AND STEEL CONSUMPTION AND GNP
PER CAPITA

pounds ot copper per person per year

•

1950

1940
•

• 1969

• 1960

1920 -

i _

-A-

1930

^ moi

11900

500 1000 1500

net tons ot steel per person per year

1950
•

1969
•

1920
•

1940

•

1960

S 1910

> 1930

/ (

1890

( 1900

0.2

500 1000 1500 2000 2500 3000 3500

GNP per capita (1958 dollars per person per year)

Per capita copper and steel consumption in the United States underwent a
period ot rapid increase as total productivity rose, followed by a period ot
much slower increase after consumption reached a relatively high rate.

SOURCES: Copper and steel consumption from Metal Statistics (Somerset, NJ: American
Metal Market Company, 1970). Historical population and GNP from US Department of
Commerce, US Economic Growth (Washington, DC: Government Printing Office, 1969).

Ill

GROWTH IN THE WORLD SYSTEM

Figure 31 BIRTH RATES AND GNP PER CAPITA

births per thousand people per year

Vene

zuela

a Libya

0 Asia
a Africa
• Latin Am
o Europe,

irica

JSSR, North

America

□

vorld averag
*

0 i

* c
o*

□

■ 0 □

□

o
□

□ □

□

USSR o

□ □
□ □

° a

□

(

□

India
China
40

$1000 S2000 $3000

GNP per capita (US dollars per person per year)

Birth rates in the world's nations show a regular downward trend as GNP
per capita increases. More than one-halt of the world's people are repre-
sented in the upper left-hand corner of the graph, where GNP per capita
is less than $500 per person per year and birth rates range from 40 to 50
per thousand persons per year. The two major exceptions to the trend,
Venezuela and Libya, are oil-exporting nations, where the rise in income
is quite recent and income distribution is highly unequal.

SOURCE: US Agency for International Development, Population Program Assistance
(Washington, DC: Government Printing Office. 1970).

The maximum biological birth rate is the rate at which
women would bear children if they practiced no method of
birth control throughout their entire reproductive lifetimes.
This rate is biologically determined, depending mainly on the
general health of the population. The desired birth rate is the
rate that would result if the population practiced "perfect"

112

GROWTH IN THE WORLD SYSTEM

birth control and had only planned and wanted children. Birth
control effectiveness measures the extent to which the popula-
tion is able to achieve the desired birth rate rather than the
maximum biological one. Thus "birth control" is defined very
broadly to include any method of controlling births actually
practiced by a population, including contraception, abortion,
and sexual abstinence. It should be emphasized that perfect
birth control effectiveness does not imply low fertility. If de-
sired birth rate is high, fertility will also be high.

These three factors influencing fertility are in turn influenced
by other factors in the world system. Figure 31 suggests that
industrialization might be one of the more important of these
factors.

The relation between crude birth rates and GNP per capita
of all the nations in the world follows a surprisingly regular
pattern. In general, as GNP rises, the birth rate falls. This
appears to be true, despite differences in religious, cultural, or
political factors. Of course, we cannot conclude from this figure
that a rising GNP per capita directly causes a lower birth rate.
Apparently, however, a number of social and educational
changes that ultimately lower the birth rate are associated with
increasing industrialization. These social changes typically
occur only after a rather long delay.

Where in the feedback loop structure does this inverse rela-
tionship between birth rate and per capita GNP operate ? Most
evidence would indicate that it does not operate through the
maximum biological birth rate. If anything, rising industriali-
zation implies better health, so that the number of births
possible might increase as GNP increases. On the other hand,
birth control effectiveness would also increase, and this effect
certainly contributes to the decline in births shown in figure 31.

113

GROWTH IN THE WORLD SYSTEM.

Figure 32 FAMILIES WANTING FOUR OR MORE
CHILDREN AND GNP PER CAPITA

percent ol population

-*-=

►

500 1000 1500 2000 2500 3000

GNP pee cap/la (US dollars per person per year)

Respondents to family planning surveys in seventeen different countries
indicated how many children they would like to have. The percentage of
respondents desiring large families (tour or more children) shows a rela-
tionship to average GNP per capita comparable to the trend shown In
figure 31.

SOURCE: Bernard Berelson et al . Family Planning and Population Programs (Chicago:
University of Chicago Press, 1965).

We suggest, however, that the major effect of rising GNP is
on the desired birth rate. Evidence for this suggestion is shown
in figure 32. The curve indicates the percentage of respondents
to family planning surveys wanting more than four children
as a function of GNP per capita. The general shape of the
curve is similar to that of figure 31, except for the slight in-
crease in desired family size at high incomes.

The economist J. J. Spengler has explained the general
response of desired birth rate to income in terms of the eco-
nomic and social changes that occur during the process of

GROWTH IN THE WORLD SYSTEM

Figure 33 DESIRED FAMILY SIZE

"value" ol each child

Schematic representation ol the economic determinants of family size
follows a rough cost-benefit analysis. The resultant curve summarizes the
balance between value and cost of children and resources available for
child-raising, all as a function of increasing industrialization. This com-
posite curve is similar to the curves In figures 31 and 32.

industrialization. 32 He believes that each family, consciously
or unconsciously, weighs the value and cost of an additional
child against the resources the family has available to devote to
that child. This process results in a general attitude about
family size that shifts as income increases, as shown in figure 33.

115

GROWTH IN THE WORLD SYSTEM

The "value" of a child includes monetary considerations,
such as the child's labor contribution to the family farm or
business and the eventual dependence on the child's support
when the parents reach old age. As a country becomes indus-
trialized, child labor laws, compulsory education, and social
security provisions all reduce the potential monetary value of a
child. "Value" also includes the more intangible values of a
child as an object of love, a carrier of the family name, an
inheritor of the family property, and a proof of masculinity.
These values tend to be important in any society, and so the
reward function always has a positive value. It is particularly
important in poor societies, where there are almost no alter-
native modes of personal gratification.

The "cost" of a child includes the actual financial outlays
necessary to supply the child's needs, the opportunity costs of
the mother's time devoted to child care, and the increased
responsibility and decreased freedom of the family as a whole.
The cost of children is very low in a traditional society. No
additional living space is added to house a new child, little
education or medical care is available, clothing and food
requirements are minimal. The mother is generally uneducated
and assigns no value to her time. The family has little freedom
to do anything that a child would hinder, and the extended
family structure is there to provide child care if it should
become necessary, for example, for a parent to leave home to
find a job.

As family income increases, however, children are given
more than the basic food and clothing requirements. They
receive better housing and medical care, and education becomes
both necessary and expensive. Travel, recreation, and alterna-
tive employment for the mother become possibilities that are

116

GROWTH IN THE WORLD SYSTEM

not compatible with a large family. The extended family struc-
ture tends to disappear with industrialization, and substitute
child care is costly.

The "resources" that a family has to devote to a child gen-
erally increase with income. At very high income, the value
and cost curves become nearly invariant with further increases
in income, and the resource curve becomes the dominant factor
in the composite desired birth rate. Thus, in rich countries,
such as the United States, desired family size becomes a direct
function of income. It should be noted that "resources" is
partially a psychological concept in that present actual income
must be modified by an expectation of future income in plan-
ning family size.

We have summarized all these social factors by a feedback
loop link between industrial output per capita and desired
birth rate. The general shape of the relationship is shown on
the right side of figure 33. We do not mean to imply by this
link that rising income is the only determinant of desired
family size, or even that it is a direct determinant. In fact we
include a delay between industrial output per capita and
desired family size to indicate that this relationship requires a
social adjustment, which may take a generation or two to
complete. Again, this relationship may be altered by future
policies or social changes. As it stands it simply reflects the
historical behavior of human society. Wherever economic de-
velopment has taken place, birth rates have fallen. Where
industrialization has not occurred, birth rates have remained
high.

Pollution effect on lifetime

We have included in the world model the possibility that

117

GROWTH IN THE WORLD SYSTEM

pollution will influence the life expectancy of the world's
population. We express this relationship by a "lifetime multi-
plier from pollution," a function that multiplies the life expec-
tancy otherwise indicated (from the values of food and medical
services) by the contribution to be expected from pollution.
If pollution were severe enough to lower the life expectancy
to 90 percent of its value in the absence of pollution, the
multiplier would equal 0.9. The relationship of pollution to
life expectancy is diagramed below.

There are only meager global data on the effect of pollution
on life expectancy. Information is slowly becoming available
about the toxicity to humans of specific pollutants, such as
mercury and lead. Attempts to relate statistically a given
concentration of pollutant to the mortality of a population
have been made only in the field of air pollution. 33

Although quantitative evidence is not yet available, there is
little doubt that a relationship does indeed exist between pollu-
tion and human health. According to a recent Council on En-
vironmental Quality report:

Serious air pollution episodes have demonstrated how air pollution can
severely impair health. Further research is spawning a growing body
of evidence which indicates that even the long-term effects of exposure
to low concentrations of pollutants can damage health and cause chronic
disease and premature death, especially for the most vulnerable — the
aged and those already suffering from respiratory diseases. Major ill-
nesses linked to air pollution include emphysema, bronchitis, asthma,
and lung cancer. 34

life expectancy

lifetime
multiplier

from
pollution

pollution

118

GROWTH IN THE WORLD SYSTEM

What will be the effect on human lifetime as the present
level of global pollution increases? We cannot answer this
question accurately, but we do know that there will be some
effect. We would be more in error to ignore the influence of
pollution on life expectancy in the world model than to include
it with our best guess of its magnitude. Our approach to a
"best guess" is explained below and illustrated in figure 34.

If an increase in pollution by a factor of 100 times the present
global level would have absolutely no effect on lifetime, the
straight line A in figure 34 would be the correct representation
of the relationship we seek. Life expectancy would be unre-
lated to pollution. Curve A is very unlikely, of course, since
we know that many forms of pollution are damaging to the
human body. Curve B or any similar curve that rises above
curve A is even more unlikely since it indicates that additional
pollution will increase average lifetime. We can expect that
the relationship between pollution and lifetime is negative,
although we do not know what the exact shape or slope of a
curve expressing it will be. Any one of the curves labeled C,
or any other negative curve, might represent the correct
function.

Our procedure in a case like this is to make several different
estimates of the probable effect of one variable on another and
then to test each estimate in the model. If the model behavior
is very sensitive to small changes in a curve, we know we
must obtain more information before including it. If (as in
this case) the behavior mode of the entire model is not sub-
stantially altered by changes in the curve, we make a conserva-
tive guess of its shape and include the corresponding values in
our calculation. Curve C" in figure 34 is the one we believe
most accurately depicts the relationship between life expectancy

119

GROWTH IN THE WORLD SYSTEM

Figure 34 THE EFFECT OF POLLUTION ON LIFETIME

lifetime multiplier from pollution

0.5

1 A

\c-

>. C"

25 SO 75 100

average pollution level

The relationship between level of pollution and average human lifetime
might follow many different curves. Curve A indicates that pollution has
no effect on lifetime (normal life expectancy is multiplied by 1.0). Curve B
represents an enhancement of lifetime as pollution increases (normal life
expectancy is multiplied by a number greater than 1.0). The curves C, C,
and C" reflect differing assumptions about deleterious effects of pollu-
tion on lifetime. The relationship used in the world model is shaped like
curve C".

and pollution. This curve assumes that an increase in global
pollution by a factor of 10 would have almost no effect on
lifetime but an increase by a factor of 100 would have a great
effect.

120

GROWTH IN THE WORLD SYSTEM

The usefulness of the world model

The relationships discussed above comprise only three of the
hundred or so causal links that make up the world model.
They have been chosen for presentation here as examples of
the kind of information inputs we have used and the way
in which we have used them. In many cases the information
available is not complete. Nevertheless, we believe that the
model based on this information is useful even at this pre-
liminary stage for several reasons.

First, we hope that by posing each relationship as a hypoth-
esis, and emphasizing its importance in the total world system,
we may generate discussion and research that will eventually
improve the data we have to work with. This emphasis is
especially important in the areas in which different sectors
of the model interact (such as pollution and human lifetime),
where interdisciplinary research will be necessary.

Second, even in the absence of improved data, information
now available is sufficient to generate valid basic behavior
modes for the world system. This is true because the model's
feedback loop structure is a much more important determinant
of overall behavior than the exact numbers used to quantify
the feedback loops. Even rather large changes in input data
do not generally alter the mode of behavior, as we shall see
in the following pages. Numerical changes may well affect the
period of an oscillation or the rate of growth or the time of a
collapse, but they will not affect the fact that the basic mode
is oscillation or growth or collapse.* Since we intend to use the

• The importance of structure rather than numbers is a most difficult
concept to present without extensive examples from the observation and
modeling of dynamic systems. For further discussion of this point, see
chapter 6 of J. W. Forrester's Urban Dynamics (Cambridge, Mass.: MIT
Press, 1969).

121

GROWTH IN THE WORLD SYSTEM

world model only to answer questions about behavior modes,
not to make exact predictions, we are primarily concerned
with the correctness of the feedback loop structure and only
secondarily with the accuracy of the data. Of course when
we do begin to seek more detailed, short-term knowledge,
exact numbers will become much more important.

Third, if decision-makers at any level had access to precise
predictions and scientifically correct analyses of alternate poli-
cies, we would certainly not bother to construct or publish a
simulation model based on partial knowledge. Unfortunately,
there is no perfect model available for use in evaluating today's
important policy issues. At the moment, our only alternatives
to a model like this, based on partial knowledge, are mental
models, based on the mixture of incomplete information and
intuition that currently lies behind most political decisions.
A dynamic model deals with the same incomplete information
available to an intuitive model, but it allows the organization
of information from many different sources into a feedback
loop structure that can be exactly analyzed. Once all the
assumptions are together and written down, they can be
exposed to criticism, and the system's response to alternative
policies can be tested.

WORLD MODEL BEHAVIOR

Now we are at last in a position to consider seriously the
questions we raised at the beginning of this chapter. As the
world system grows toward its ultimate limits, what will be
its most likely behavior mode? What relationships now exis-
tent will change as the exponential growth curves level off?
What will the world be like when growth comes to an end ?
There are, of course, many possible answers to these ques-

122

GROWTH IN THE WORLD SYSTEM

tions. We will examine several alternatives, each dependent
on a different set of assumptions about how human society will
respond to problems arising from the various limits to growth.

Let us begin by assuming that there will be in the future no
great changes in human values nor in the functioning of the
global population-capital system as it has operated for the last
one hundred years. The results of this assumption are shown in
figure 35. We shall refer to this computer output as the "stan-
dard run" and use it for comparison with the runs based on
other assumptions that follow. The horizontal scale in figure
35 shows time in years from 1900 to 2100. With the computer
we have plotted the progress over time of eight quantities:

population (total number of persons)
industrial output per capita (dollar equivalent per

person per year)
food per capita (kilogram-grain equivalent per per-
son per year)
pollution (multiple of 1970 level)
— •— •— nonrenewable resources (fraction of 1900 reserves
remaining)

B crude birth rate (births per 1000 persons per year)
D crude death rate (deaths per 1000 persons per year)
S services per capita (dollar equivalent per person per
year)

Each of these variables is plotted on a different vertical scale.
We have deliberately omitted the vertical scales and we have
made the horizontal time scale somewhat vague because we
want to emphasize the general behavior modes of these com-
puter outputs, not the numerical values, which are only approxi-

123

GROWTH IN THE WORLD SYSTEM

Figure 35 WORLD MODEL STANDARD RUN

The "standard" world model run assumes no major change in the physical,
economic, or social relationships that have historically governed the de-
velopment of the world system. All variables plotted here follow historical
values from 1900 to 1970. Food, industrial output, and population grow
exponentially until the rapidly diminishing resource base forces a slowdown
in industrial growth. Because of natural delays in the system, both popu-
lation and pollution continue to increase for some time after the peak of
industrialization. Population growth is finally halted by a rise in the death
rate due to decreased food and medical services.

mately known. The scales are, however, exactly equal in all
the computer runs presented here, so results of different runs
may be easily compared.

124

GROWTH IN THE WORLD SYSTEM

All levels in the model (population, capital, pollution, etc.)
begin with 1900 values. From 1900 to 1970 the variables plotted
in figure 35 (and numerous other variables included in the
model but not plotted here) agree generally with their his-
torical values to the extent that we know them. Population
rises from 1.6 billion in 1900 to 3.5 billion in 1970. Although
the birth rate declines gradually, the death rate falls more
quickly, especially after 1940, and the rate of population
growth increases. Industrial output, food, and services per
capita increase exponentially. The resource base in 1970 is still
about 95 percent of its 1900 value, but it declines dramatically
thereafter, as population and industrial output continue to
grow.

The behavior mode of the system shown in figure 35 is
clearly that of overshoot and collapse. In this run the collapse
occurs because of nonrenewable resource depletion. The indus-
trial capital stock grows to a level that requires an enormous
input of resources. In the very process of that growth it depletes
a large fraction of the resource reserves available. As resource
prices rise and mines are depleted, more and more capital must
be used for obtaining resources, leaving less to be invested for
future growth. Finally investment cannot keep up with depre-
ciation, and the industrial base collapses, taking with it the
service and agricultural systems, which have become dependent
on industrial inputs (such as fertilizers, pesticides, hospital
laboratories, computers, and especially energy for mechaniza-
tion). For a short time the situation is especially serious because
population, with the delays inherent in the age structure and
the process of social adjustment, keeps rising. Population finally
decreases when the death rate is driven upward by lack of food
and health services.

125

GROWTH IN THE WORLD SYSTEM

The exact timing of these events is not meaningful, given
the great aggregation and many uncertainties in the model.
It is significant, however, that growth is stopped well before
the year 2100. We have tried in every doubtful case to make
the most optimistic estimate of unknown quantities, and we
have also ignored discontinuous events such as wars or epi-
demics, which might act to bring an end to growth even
sooner than our model would indicate. In other words, the
model is biased to allow growth to continue longer than it
probably can continue in the real world. We can thus say with
some confidence that, under the assumption of no major
change in the present system, population and industrial growth
will certainly stop within the next century, at the latest.

The system shown in figure 35 collapses because of a resource
crisis. What if our estimate of the global stock of resources is
wrong? In figure 35 we assumed that in 1970 there was a
250-year supply of all resources, at 1970 usage rates. The static
reserve index column of the resource table in chapter II will
verify that this assumption is indeed optimistic. But let us be
even more optimistic and assume that new discoveries or ad-
vances in technology can double the amount of resources eco-
nomically available. A computer run under that assumption
is shown in figure 36.

The overall behavior mode in figure 36 — growth and col-
lapse — is very similar to that in the standard run. In this case
the primary force that stops growth is a sudden increase in
the level of pollution, caused by an overloading of the natural
absorptive capacity of the environment. The death rate rises
abruptly from pollution and from lack of food. At the same
time resources are severely depleted, in spite of the doubled
amount available, simply because a few more years of expo-

GROWTH IN THE WORLD SYSTEM

Figure 36 WORLD MODEL WITH NATURAL RESOURCE
RESERVES DOUBLED

To test the model assumption about available resources, we doubled the
resource reserves in 1900, keeping all other assumptions identical to those
in the standard run. Now industrialization can reach a higher level since
resources are not so quickly depleted. The larger industrial plant releases
pollution at such a rate, however, that the environmental pollution absorp-
tion mechanisms become saturated. Pollution rises very rapidly, causing
an immediate increase in the death rate and a decline in food production.
At the end of the run resources are severely depleted in spite of the
doubled amount initially available.

nential growth in industry are sufficient to consume those extra
resources.

Is the future of the world system bound to be growth and
then collapse into a dismal, depleted existence? Only if we

127

GROWTH IN THE WORLD SYSTEM

make the initial assumption that our present way of doing
things will not change. We have ample evidence of mankind's
ingenuity and social flexibility. There are, of course, many
likely changes in the system, some of which are already taking
place. The Green Revolution is raising agricultural yields in
nonindustrialized countries. Knowledge about modern meth-
ods of birth control is spreading rapidly. Let us use the world
model as a tool to test the possible consequences of the new
technologies that promise to raise the limits to growth.

128

CHAPTER IV

TECHNOLOGY

AND

THE

LIMITS

GROWTH

Towards what ultimate point is society
tending by its industrial progress? When
the progress ceases, in what condition
are we to expect that it will leave
mankind?

JOHN STUART MILL, 1857

Although the history of human ef-
fort contains numerous incidents of mankind's failure to live
within physical limits, it is success in overcoming limits that
forms the cultural tradition of many dominant people in
today's world. Over the past three hundred years, mankind
has compiled an impressive record of pushing back the appar-
ent limits to population and economic growth by a series of
spectacular technological advances. Since the recent history
of a large part of human society has been so continuously
successful, it is quite natural that many people expect techno-
logical breakthroughs to go on raising physical ceilings indefi-
nitely. These people speak about the future with resounding
technological optimism.

129

TECHNOLOGY AND THE LIMITS TO GROWTH

There are no substantial limits in sight either in raw materials or
in energy that alterations in the price structure, product substitution,
anticipated gains in technology and pollution control cannot be expected
to solve. 35

Given the present capacity of the earth for food production, and the
potential for additional food production if modern technology were
more fully employed, the human race clearly has within its grasp the
capacity to chase hunger from the earth — within a matter of a decade
or two. 39

Humanity's mastery of vast, inanimate, inexhaustible energy sources
and the accelerated doing more with less of sea, air, and space technology
has proven Malthus to be wrong. Comprehensive physical and economic
success for humanity may now be accomplished in one-fourth of a
century. 37

Can statements like these be reconciled with the evidence for
the limits to growth we have discussed here ? Will new tech-
nologies alter the tendency of the world system to grow and
collapse? Before accepting or rejecting these optimistic views
of a future based on technological solutions to mankind's
problems, one would like to know more about the global
impact of new technologies, in the short term and the long
term, and in all five interlocking sectors of the population-
capital system.

TECHNOLOGY IN THE WORLD MODEL

There is no single variable called "technology" in the world
model. We have not found it possible to aggregate and gen-
eralize the dynamic implications of technological development
because different technologies arise from and influence quite
different sectors of the model. Birth control pills, high-yield
grains, television, and off-shore oil-drilling rigs can all be
considered technological developments, but each plays a dis-
tinct role in altering the behavior of the world system. There-

130

TECHNOLOGY AND THE LIMITS TO GROWTH

fore we must represent each proposed technology separately in
the model, considering carefully how it might affect each of
the assumptions we have made about the model elements. In
this section we shall present some examples of this approach to
global, long-term "technology assessment."

Energy and resources

The technology of controlled nuclear fission has already lifted
the impending limit of fossil fuel resources. It is also possible
that the advent of fast breeder reactors and perhaps even fusion
nuclear reactors will considerably extend the lifetime of fission-
able fuels, such as uranium. Does this mean that man has mas-
tered "vast, inanimate, inexhaustible energy sources" that will
release unlimited raw materials for his industrial plants ? What
will be the effect of increasing use of nuclear power on resource
availability in the world system ?

Some experts believe that abundant energy resources will en-
able mankind to discover and utilize otherwise inaccessible
materials (in the sea bed, for example) ; to process poorer ores,
even down to common rock; and to recycle solid waste and
reclaim the metals it contains. Although this is a common be-
lief, it is by no means a universal one, as the following quota-
tion by geologist Thomas Lovering indicates.

Cheaper energy, in fact, would little reduce the total costs (chiefly
capital and labor) required for mining and processing rock. The enor-
mous quantities of unusable waste produced for each unit of metal in
ordinary granite (in a ratio of at least 2,000 to 1) are more easily dis-
posed of on a blueprint than in the field. ... To recover minerals
sought, the rock must be shattered by explosives, drilled for input and
recovery wells, and flooded with solutions containing special extractive
chemicals. Provision must then be made to avoid the loss of solutions
and the consequent contamination of groundwater and surface water.
These operations will not be obviated by nuclear power. 38

131

TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 37 WORLD MODEL WITH "UNLIMITED" RESOURCES

The problem of resource depletion In the world model system Is eliminated
by two assumptions: first, that "unlimited" nuclear power will double the
resource reserves that can be exploited and, second, that nuclear energy
will make extensive programs of recycling and substitution possible. It
these changes are the only ones Introduced in the system, growth Is
stopped by rising pollution, as it was in figure 36.

Let us assume, however, that the technological optimists are
correct and that nuclear energy will solve the resource prob-
lems of the world. The result of including that assumption in
the world model is shown in figure 37. To express the pos-
sibility of utilizing lower grade ore or mining the seabed, we
have doubled the total amount of resources available, as in

132

TECHNOLOGY AND THE LIMITS TO GROWTH

figure 36. We have also assumed that, starting in 1975, pro-
grams of reclamation and recycling will reduce the input of
virgin resources needed per unit of industrial output to only
one-fourth of the amount used today. Both of these assump-
tions are, admittedly, more optimistic than realistic.

In figure 37 resource shortages indeed do not occur. Growth
is stopped by rising pollution, as it was in figure 36. The ab-
sence of any constraint from resources allows industrial output,
food, and services to rise slightly higher than in figure 36 before
they fall. Population reaches about the same peak level as it did
in figure 36, but it falls more suddenly and to a lower final
value.

"Unlimited" resources thus do not appear to be the key to
sustaining growth in the world system. Apparently the eco-
nomic impetus such resource availability provides must be ac-
companied by curbs on pollution if a collapse of the world
system is to be avoided.

Pollution control

We assumed in figure 37 that the advent of nuclear power
neither increased nor decreased the average amount of pollu-
tion generated per unit of industrial output. The ecological
impact of nuclear power is not yet clear. While some by-prod-
ucts of fossil fuel consumption, such as C0 2 and sulfur dioxide,
will be decreased, radioactive by-products will be increased.
Resource recycling will certainly decrease pollution from solid
waste and from some toxic metals. However, a changeover to
nuclear power will probably have little effect on most other
kinds of pollution, including by-products of most manufactur-
ing processes, thermal pollution, and pollution arising from
agricultural practices.

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TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 38 COST OF POLLUTION REDUCTION

dollars per pound

10 20 30 40 50 60 70 80 90 100

biological oxygen demand reduction (percent)

Incremental cost of reducing organic wastes from a 2,700-ton-per-day beet
sugar plant rises steeply as emission standards approach complete purity.
Reduction of biological oxygen demand (a measure ot the oxygen required
to decompose wastes) costs less than $1 a pound up to 30 percent reduc-
tion. Reduction beyond 65 percent requires more than $20 tor each addi-
tional pound removed, and at 95 percent reduction, each pound removed
costs $60.

SOURCE: Second Annual Report ol Ihe Council on Environmental Quality (Washington, DC:
Government Printing Office, 1971).

It is likely, however, that a world society with readily
available nuclear power would be able to control industrial
pollution generation by technological means. Pollution con-
trol devices are already being developed and installed on a large
scale in industrialized areas. How would the model behavior

TECHNOLOGY AND THE LIMITS TO GROWTH

be changed if a policy of strict pollution control were instituted
in, say, 1975?

Strict pollution control does not necessarily mean total pol-
lution control. It is impossible to eliminate all pollution be-
cause of both technological and economic constraints. Econom-
ically, the cost of pollution control soars as emission standards
become more severe. Figure 38 shows the cost of reducing
water pollution from a sugar-processing plant as a function of
organic wastes removed. If no organic wastes were allowed to
leave the plant, the cost would be 100 times greater than if only
30 percent of the wastes were removed from the effluent. Table
6 below shows a similar trend in the projected costs of reduc-
ing air pollution in a US city. 39

. In figure 39 the world model output is plotted assuming both
the reduction in resource depletion of figure 37 and a reduction
in pollution generation from all sources by a factor of four,

Table 6 COST OF REDUCING AIR POLLUTION IN A US CITY

Percent reduction Percent reduction Projected

in SO, in pardcuUtet cost

starting in 1975. Reduction to less than one-fourth of the present
rate of pollution generation is probably unrealistic because of
cost, and because of the difficulty of eliminating some kinds
of pollution, such as thermal pollution and radioisotopes from
nuclear power generation, fertilizer runoff, and asbestos par-
ticles from brake linings. We assume that such a sharp reduc-

42
48

22
66
69

50,000
7,500,000
26,000,000

135

TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 39 WORLD MODEL WITH "UNLIMITED" RESOURCES
AND POLLUTION CONTROLS

A further technological improvement is added to the world model in 1975
to avoid the resource depletion and pollution problems of previous model
runs. Here we assume that pollution generation per unit of industrial and
agricultural output can be reduced to one-fourth of its 1970 value. Re-
source policies are the same as those in figure 37. These changes allow
population and industry to grow until the limit of arable land is reached.
Food per capita declines, and industrial growth is also slowed as capital
is diverted to food production.

tion in pollution generation could occur globally and quickly
for purposes of experimentation with the model, not because
wc believe it is politically feasible, given our present institu-
tions.

136

TECHNOLOGY AND THE LIMITS TO GROWTH

As figure 39 shows, the pollution control policy is indeed
successful in averting the pollution crisis of the previous run.
Both population and industrial output per person rise well be-
yond their peak values in figure 37, and yet resource depletion
and pollution never become problems. The overshoot mode is
still operative, however, and the collapse comes about this time
from food shortage.

As long as industrial output is rising in figure 39, the yield
from each hectare of land continues to rise (up to a maximum
of seven times the average yield in 1900) and new land is de-
veloped. At the same time, however, some arable land is taken
for urban-industrial use, and some land is eroded, especially by
highly capitalized agricultural practices. Eventually the limit
of arable land is reached. After that point, as population con-
tinues to rise, food per capita decreases. As the food shortage
becomes apparent, industrial output is diverted into agricultural
capital to increase land yields. Less capital is available for in-
vestment, and finally the industrial output per capita begins
to fall. When food per capita sinks to the subsistence level, the
death rate begins to increase, bringing an end to population
growth.

Increased food yield and birth control

The problem in figure 39 could be viewed either as too little
food or as too many people. The technological response to the
first situation would be to produce more food, perhaps by some
further extension of the principles of the Green Revolution.
(The development of the new, high-yield grain varieties which
constitutes the Green Revolution has been included in the
original model equations.) The technological solution to the
second problem would be to provide better methods of birth

137

TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 40 WORLD MODEL WITH "UNLIMITED" RESOURCES,
POLLUTION CONTROLS, AND INCREASED
AGRICULTURAL PRODUCTIVITY

To avoid the tood crisis of the previous model run, average land yield Is
doubled in 1975 in addition to the pollution and resource policies of pre-
vious figures. The combination of these three policies removes so many
constraints to growth that population and industry reach very high levels.
Although each unit of industrial production generates much less pollution,
total production rises enough to create a pollution crisis that brings an end
to growth.

control. The results of these two changes, instituted in 1975
along with the changes in resource use and pollution genera-
tion we have already discussed, are shown both separately and
simultaneously in figures 40, 41, and 42.
In figure 40 we assume that the normal yield per hectare of

138

TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 41 WORLD MODEL WITH "UNLIMITED" RESOURCES,
POLLUTION CONTROLS, AND "PERFECT" BIRTH CONTROL

Instead of an increase in food production, an Increase in birth control
effectiveness is tested as a policy to avert the food problem. Since the birth
control is voluntary and does not involve any value changes, population
continues to grow, but more slowly than It did in figure 39. Nevertheless,
the food crisis is postponed for only a decade or two.

all the world's land can be further increased by a factor of two.
The result is an enormous increase in food, industrial output,
and services per capita. Average industrial output per person
for all the world's people becomes nearly equal to the 1970 US
level, but only briefly. Although a strict pollution control
policy is still in effect, so that pollution per unit of output is

139

TECHNOLOGY AND THE LIMITS TO GROWTH

Figure 42 WORLD MODEL WITH "UNLIMITED" RESOURCES,
POLLUTION CONTROLS, INCREASED AGRICULTURAL
PRODUCTIVITY, AND "PERFECT' BIRTH CONTROL

Four simultaneous technological policies are introduced in the world
model in an attempt to avoid the growth-and-collapse behavior of previous
runs. Resources are fully exploited, and 75 percent ot those used are re-
cycled. Pollution generation is reduced to one-fourth of its 1970 value.
Land yields are doubled, and effective methods ot birth control are made
available to the world population. The result is a temporary achievement
of a constant population with a world average income per capita that
reaches nearly the present US level. Finally, though, industrial growth is
halted, and the death rate rises as resources are depleted, pollution accu-
mulates, and food production declines.

reduced by a factor of four, industry grows so quickly that soon
it is producing four times as much output. TTius the level of
pollution rises in spite of the pollution control policy, and a

140

TECHNOLOGY AND THE LIMITS TO GROWTH

pollution crisis stops further growth, as it did in figure 37.

Figure 41 shows the alternate technological policy — perfect
birth control, practiced voluntarily, starting in 1975. The result
is not to stop population growth entirely because such a policy
prevents only the births of unwanted children. The birth rate
does decrease markedly, however, and the population grows
more slowly than it did in figures 39 and 40. In this run
growth is stopped by a food crisis occurring about 20 years
later than in figure 39.

In figure 42 we apply increased land yield and perfect birth
control simultaneously. Here we are utilizing a technological
policy in every sector of the world model to circumvent in
some way the various limits to growth. The model system is
producing nuclear power, recycling resources, and mining the
most remote reserves; withholding as many pollutants as pos-
sible; pushing yields from the land to undreamed-of heights;
and producing only children who are actively wanted by their
parents. The result is still an end to growth before the year
2100. In this case growth is stopped by three simultaneous
crises. Overuse of land leads to erosion, and food production
drops. Resources are severely depleted by a prosperous world
population (but not as prosperous as the present US popula-
tion). Pollution rises, drops, and then rises again dramatically,
causing a further decrease in food production and a sudden
rise in the death rate. The application of technological solu-
tions alone has prolonged the period of population and indus-
trial growth, but it has not removed the ultimate limits to that
growth.

The overshoot mode

Given the many approximations and limitations of the world
model, there is no point in dwelling glumly on the series of

141

TECHNOLOGY AND THE LIMITS TO GROWTH

catastrophes it tends to generate. We shall emphasize just one
more time that none of these computer outputs is a prediction.
We would not expect the real world to behave like the world
model in any of the graphs we have shown, especially in the
collapse modes. The model contains dynamic statements about
only the physical aspects of man's activities. It assumes that
social variables — income distribution, attitudes about family
size, choices among goods, services, and food — will continue
to follow the same patterns they have followed throughout the
world in recent history. These patterns, and the human values
they represent, were all established in the growth phase of our
civilization. They would certainly be greatly revised as popula-
tion and income began to decrease. Since we find it difficult
to imagine what new forms of human societal behavior might
emerge and how quickly they would emerge under collapse
conditions, we have not attempted to model such social
changes. What validity our model has holds up only to the
point in each output graph at which growth comes to an end
and collapse begins.

Although we have many reservations about the approxima-
tions and simplifications in the present world model, it has led
us to one conclusion that appears to be justified under all the
assumptions we have tested so far. The basic behavior mode
of the world system is exponential growth of population and
capital, followed by collapse. As we have shown in the model
runs presented here, this behavior mode occurs if we assume no
change in the present system or if we assume any number of
technological changes in the system.

The unspoken assumption behind all of the model runs we
have presented in this chapter is that population and capital
growth should be allowed to continue until they reach some

142

TECHNOLOGY AND THE LIMITS TO GROWTH

"natural" limit. This assumption also appears to be a basic part
of the human value system currently operational in the real
world. Whenever we incorporate this value into the model,
the result is that the growing system rises above its ultimate
limit and then collapses. When we introduce technological de-
velopments that successfully lift some restraint to growth or
avoid some collapse, the system simply grows to another limit,
temporarily surpasses it, and falls back. Given that first assump-
tion, that population and capital growth should not be deliber-
ately limited but should be left to "seek their own levels," we
have not been able to find a set of policies that avoids the col-
lapse mode of behavior.

It is not really difficult to understand how the collapse mode
comes about. Everywhere in the web of interlocking feedback
loops that constitutes the world system we have found it neces-
sary to represent the real-world situation by introducing time
delays between causes and their ultimate effects. These are nat-
ural delays that cannot be controlled by technological means.
They include, for example, the delay of about fifteen years be-
tween the birth of a baby and the time that baby can first re-
produce itself. The time delay inherent in the aging of a
population introduces a certain unavoidable lag in the ability
of the population to respond through the birth rate to chang-
ing conditions. Another delay occurs between the time a pol-
lutant is released into the environment and the time it has a
measurable influence on human health. This delay includes
the passage of the pollutant through air or rivers or soil and
into the food chain, and also the time from human ingestion
or absorption of the pollutant until clinical symptoms appear.
This second delay may be as long as 20 years in the case of
some carcinogens. Other delays occur because capital cannot

143

TECHNOLOGY AND THE LIMITS TO GROWTH

be transferred instantly from one sector to another to meet
changing demands, because new capital and land can only be
produced or developed gradually, and because pollution can
only slowly be dispersed or metabolized into harmless forms.

Delays in a dynamic system have serious effects only if
the system itself is undergoing rapid changes. Perhaps a simple
example will clarify that statement. When you drive a car
there is a very short, unavoidable delay between your percep-
tion of the road in front of you and your reaction to it. There
is a longer delay between your action on the accelerator or
brakes and the car's response to that action. You have learned
to deal with those delays. You know that, because of the delays,
it is unsafe to drive too fast. If you do, you will certainly
experience the overshoot and collapse mode, sooner or later.
If you were blindfolded and had to drive on the instructions
of a front-seat passenger, the delay between perception and
action would be considerably lengthened. The only safe way
to handle the extended delay would be to slow down. If you
tried to drive your normal speed, or if you tried to accelerate
continuously (as in exponential growth), the result would be
disastrous.

In exactly the same way, the delays in the feedback loops
of the world system would be no problem if the system were
growing very slowly or not at all. Under those conditions any
new action or policy could be instituted gradually, and the
changes could work their way through the delays to feed back
on every part of the system before some other action or policy
would have to be introduced. Under conditions of rapid
growth, however, the system is forced into new policies and
actions long before the results of old policies and actions can
be properly assessed. The situation is even worse when the

144

TECHNOLOGY AND THE LIMITS TO GROWTH

growth is exponential and the system is changing ever more
rapidly.

Thus population and capital, driven by exponential growth,
not only reach their limits, but temporarily shoot beyond them
before the rest of the system, with its inherent delays, reacts
to stop growth. Pollution generated in exponentially increas-
ing amounts can rise past the danger point, because the danger
point is first perceived years after the offending pollution was
released. A rapidly growing industrial system can build up a
capital base dependent on a given resource and then discover
that the exponentially shrinking resource reserves cannot sup-
port it. Because of delays in the age structure, a population will
continue to grow for as long as 70 years, even after average
fertility has dropped below the replacement level (an average
of two children for each married couple).

TECHNOLOGY IN THE REAL WORLD

The hopes of the technological optimists center on the ability
of technology to remove or extend the limits to growth of
population and capital. We have shown that in the world
model the application of technology to apparent problems of
resource depletion or pollution or food shortage has no impact
on the essential problem, which is exponential growth in a
finite and complex system. Our attempts to use even the most
optimistic estimates of the benefits of technology in the model
did not prevent the ultimate decline of population and indus-
try, and in fact did not in any case postpone the collapse
beyond the year 2100. Before we go on in the next chapter
to test other policies, which are not technological, let us extend
our discussion of technological solutions to some aspects of
technology that could not be included in the world model.

145

TECHNOLOGY AND THE LIMITS TO GROWTH

Technological side-effects

Dr. Garrett Hardin has defined side-effects as "effects which
I hadn't foreseen or don't want to think about." 40 He has sug-
gested that, since such effects are actually inseparable from the
principal effect, they should not be labeled side-efizcls at all.
Every new technology has side-effects, of course, and one of the
main purposes of model-building is to anticipate those effects.
The model runs in this chapter have shown some of the side-
effects of various technologies on the world's physical and
economic systems. Unfortunately the model does not indicate,
at this stage, the social side-effects of new technologies. These
effects are often the most important in terms of the influence
of a technology on people's lives.

A recent example of social side-effects from a successful new
technology appeared as the Green Revolution was introduced
to the agrarian societies of the world. The Green Revolution —
the utilization of new seed varieties, combined with fertilizers
and pesticides — was designed to be a technological solution to
the world's food problems. The planners of this new agricul-
tural technology foresaw some of the social problems it might
raise in traditional cultures. The Green Revolution was in-
tended not only to produce more food but to be labor-intensive
— to provide jobs and not to require large amounts of capital.
In some areas of the world, such as the Indian Punjab, the
Green Revolution has indeed increased the number of agri-
cultural jobs faster than the rate of growth of the total popu-
lation. In the East Punjab there was a real wage increase of
16 percent from 1963 to 1968. 41

The principal, or intended, effect of the Green Revolution —
increased food production — seems to have been achieved. Un-
fortunately the social side-effects have not been entirely bene-

146

TECHNOLOGY AND THE LIMITS TO GROWTH

ficial in most regions where the new seed varieties have been
introduced. The Indian Punjab had, before the Green Revo-
lution, a remarkably equitable system of land distribution. The
more common pattern in the nonindustrialized world is a
wide range in land ownership, with most people working
very small farms and a few people in possession of the vast
majority of the land.

Where these conditions of economic inequality already exist,
the Green Revolution tends to cause widening inequality.
Large farmers generally adopt the new methods first. They
have the capital to do so and can afford to take the risk.
Although the new seed varieties do not require tractor mech-
anization, they provide much economic incentive for mechani-
zation, especially where multiple cropping requires a quick
harvest and replanting. On large farms, simple economic con-
siderations lead almost inevitably to the use of labor-displacing
machinery and to the purchase of still more land. 42 The ulti-
mate effects of this socio-economic positive feedback loop are
agricultural unemployment, increased migration to the city,
and perhaps even increased malnutrition, since the poor and
unemployed do not have the means to buy the newly produced
food.

A specific example of the social side-effects of the Green
Revolution in an area where land is unequally distributed is
described below.

A landless laborer's income in West Pakistan today is still just about
what it was five years ago, less than $100 a year. In contrast, one land-
lord with a 1,500-acre wheat farm told me when I was in Pakistan this
winter that he had cleared a net profit of more than 1100,000 on his last
harvest. 43

Statistics from Mexico, where the Green Revolution began

147

TECHNOLOGY AND THE LIMITS TO GROWTH

in the 1940's, provide another example. From 1940 to 1960 the
average growth rate of agricultural production in Mexico was
5 percent per year. From 1950 to 1960, however, the average
number of days worked by a landless laborer fell from 194 to
100, and his real income decreased from $68 to $56. Eighty
percent of the increased agricultural production came from
only 3 percent of the farms. 44

These unexpected social side-effects do not imply that the
technology of the Green Revolution was unsuccessful. They do
imply that social side-effects must be anticipated and fore-
stalled before the large-scale introduction of a new technology.

As agriculture emerges from its traditional subsistence state to mod-
ern commercial farming ... it becomes progressively more important
to ensure that adequate rewards accrue directly to the man who tills
the soil. Indeed, it is hard to sec how there can be any meaningful
modernization of food production in Latin America and Africa south
of the Sahara unless land is registered, deeded, and distributed more
equitably. 48

Such preparation for technological change requires, at the
very least, a great deal of time. Every change in the normal
way of doing things requires an adjustment time, while the
population, consciously or unconsciously, restructures its social
system to accommodate the change. While technology can
change rapidly, political and social institutions generally change
very slowly. Furthermore, they almost never change in antici-
pation of a social need, but only in response to one.

We have already mentioned the dynamic effect of physical
delays in the world model. We must also keep in mind the
presence of social delays — the delays necessary to allow society
to absorb or to prepare for a change. Most delays, physical or
social, reduce the stability of the world system and increase

148

TECHNOLOGY AND THE LIMITS TO GROWTH

the likelihood of the overshoot mode. The social delays, like
the physical ones, are becoming increasingly more critical
because the processes of exponential growth are creating addi-
tional pressures at a faster and faster rate. The world popula-
tion grew from 1 billion to 2 billion over a period of more
than one hundred years. The third billion was added in 30
years and the world's population has had less than 20 years
to prepare for its fourth billion. The fifth, sixth, and perhaps
even seventh billions may arrive before the year 2000, less than
30 years from now. Although the rate of technological change
has so far managed to keep up with this accelerated pace,
mankind has made virtually no new discoveries to increase
the rate of social (political, ethical, and cultural) change.

Problems with no technical solutions

When the cities of America were new, they grew rapidly. Land
was abundant and cheap, new buildings rose continuously, and
the population and economic output of urban regions in-
creased. Eventually, however, all the land in the city center
was filled. A physical limit had been reached, threatening to
stop population and economic growth in that section of the
city. The technological answer was the development of sky-
scrapers and elevators, which essentially removed the constraint
of land area as a factor in suppressing growth. The central
city added more people and more businesses. Then a new
constraint appeared. Goods and workers could not move in
and out of the dense center city quickly enough. Again the
solution was technological. A network of expressways, mass
transit systems, and helicopter ports on the tops of the tallest
buildings was constructed. The transportation limit was over-
come, the buildings grew taller, the population increased.

149

TECHNOLOGY AND THE LIMITS TO GROWTH

Now most of the larger US cities have stopped growing.
(Of the ten largest, five — New York, Chicago, Philadelphia,
Detroit, and Baltimore— decreased in population from 1960 to
1970. Washington, DC, showed no change. Los Angeles, Hous-
ton, Dallas, and Indianapolis continued to grow, at least in
part by annexing additional land.) 48 The wealthier people, who
have an economic choice, are moving to the ever-expanding
ring of suburbs around the cities. The central areas are char-
acterized by noise, pollution, crime, drug addiction, poverty,
labor strikes, and breakdown of social services. The quality of
life in the city core has declined. Growth has been stopped in
part by problems with no technical solutions.

A technical solution may be defined as "one that requires a
change only in the techniques of the natural sciences, demand-
ing little or nothing in the way of change in human values
or ideas of morality." 47 Numerous problems today have no
technical solutions. Examples are the nuclear arms race,
racial tensions, and unemployment. Even if society's techno-
logical progress fulfills all expectations, it may very well be a
problem with no technical solution, or the interaction of
several such problems, that finally brings an end to population
and capital growth.

A choice of limits

Applying technology to the natural pressures that the environ-
ment exerts against any growth process has been so successful
in the past that a whole culture has evolved around the prin-
ciple of fighting against limits rather than learning to live
with them. This culture has been reinforced by the apparent
immensity of the earth and its resources and by the relative
smallness of man and his activities.

150

TECHNOLOGY AND THE LIMITS TO GROWTH

But the relationship between the earth's limits and man's
activities is changing. The exponential growth curves are
adding millions of people and billions of tons of pollutants to
the ecosystem each year. Even the ocean, which once appeared
virtually inexhaustible, is losing species after species of its
commercially useful animals. Recent FAO statistics indicate
that the total catch of the world's fisheries decreased in 1969
for the first time since 1950, in spite of more mechanized and
intensive fishing practices. (Among commercial species becom-
ing increasingly scarce are Scandinavian herring, menhaden,
and Atlantic cod.) 4 *

Yet man does not seem to learn by running into the earth's
obvious limits. The story of the whaling industry (shown in
figure 43) demonstrates, for one small system, the ultimate
result of the attempt to grow forever in a limited environment.
Whalers have systematically reached one limit after another
and have attempted to overcome each one by increases in
power and technology. As a result, they have wiped out one
species after another. The outcome of this particular grow-
forever policy can only be the final extinction of both whales
and whalers. The alternative policy is the imposition of a
man-determined limit on the number of whales taken each
year, set so that the whale population is maintained at a
steady-state level. The self-imposed limit on whaling would
be an unpleasant pressure that would prevent the growth of
the industry. But perhaps it would be preferable to the gradual
disappearance of both whales and whaling industry.

The basic choice that faces the whaling industry is the same
one that faces any society trying to overcome a natural limit
with a new technology. // it better to try to live within that
limit by accepting a self-imposed restriction on growth? Or

151

TECHNOLOGY AND THE LIMITS TO GROWTH

43 MODERN WHALING

worldwide total ol whales Killed
(thousands)

blue whales killed (thousands)

Sines 1945
more and
more whales

produce .

and

n oil.

- ' ! '

/'V

/l\
A 1 1 1

II 1

I 1

- 1 1

— ' 1 — ">vT —

worldwide whale oil production
(millions ot barrels)

aversge arose tonnage ol catcher
boats (hundreds ol tons)

Catcher
boats have
become

average horsepower ol catcher
boats (thousanda)

average production per catcher.boat
Ter day's work (barrels ol whele oil )

First, the industry
killed off the

Then in the 40's
as stocks
gave out . .

They switched
to killing
fin whales.

As fin stocks
collapsed they
turned to wis .

And now,
the sperm whale
la being hunted
without limit
oh numbers —

lists I s

* Notice that whaling virtually ceased during
World War II. That time ol turmoil lor people %

152

Um i II If

TECHNOLOGY AND THE LIMITS TO GROWTH

As wild herds of whales have been destroyed, finding the survivors has
become more difficult and has required more effort. As larger whales are
killed off, smaller species are exploited to keep the industry alive. Since
there have never been species limits, however, large whales are always
taken wherever and whenever encountered. Thus small whales are used
to subsidize the extermination of large ones.

SOURCE: Roger Payne, "Among Wild Whales," in The New York Zoological Society Newt-
letter, N ovembe r 1 968.

is it preferable to go on growing until some other natural limit
arises, in the hope that at that time another technological leap
will allow growth to continue still longer? For the last several
hundred years human society has followed the second course
so consistently and successfully that the first choice has been
all but forgotten.

There may be much disagreement with the statement that
population and capital growth must stop soon. But virtually
no one will argue that material growth on this planet can go
on forever. At this point in man's history, the choice posed
above is still available in almost every sphere of human activity.
Man can still choose his limits and stop when he pleases by
weakening some of the strong pressures that cause capital and
population growth, or by instituting counterpressures, or both.
Such counterpressures will probably not be entirely pleasant.
They will certainly involve profound changes in the social and
economic structures that have been deeply impressed into
human culture by centuries of growth. The alternative is to
wait until the price of technology becomes more than society
can pay, or until the side-effects of technology suppress growth
themselves, or until problems arise that have no technical
solutions. At any of those points the choice of limits will be
gone. Growth will be stopped by pressures that are not of
human choosing, and that, as the world model suggests, may

153

TECHNOLOGY AND THE LIMITS TO GROWTH

be very much worse than those which society might choose
for itself.

We have felt it necessary to dwell so long on an analysis
of technology here because we have found that technological
optimism is the most common and the most dangerous reaction
to our findings from the world model. Technology can relieve
the symptoms of a problem without affecting the underlying
causes. Faith in technology as the ultimate solution to all
problems can thus divert our attention from the most funda-
mental problem — the problem of growth in a finite system —
and prevent us from taking effective action to solve it.

On the other hand, our intent is certainly not to brand
technology as evil or futile or unnecessary. We are technolo-
gists ourselves, working in a technological institution. We
strongly believe, as we shall point out in the following chapter,
that many of the technological developments mentioned here
— recycling, pollution control devices, contraceptives — will be
absolutely vital to the future of human society if they are
combined with deliberate checks on growth. We would deplore
an unreasoned rejection of the benefits of technology as strong-
ly as we argue here against an unreasoned acceptance of them.
Perhaps the best summary of our position is the motto of the
Sierra Club: "Not blind opposition to progress, but opposition
to blind progress."

We would hope that society will receive each new techno-
logical advance by establishing the answers to three questions
before the technology is widely adopted. The questions are:

1. What will be the side-effects, both physical and social, if
this development is introduced on a large scale?

2. What social changes will be necessary before this develop-

154

TECHNOLOGY AND THE LIMITS TO GROWTH

mcnt can be implemented properly, and how long will it take
to achieve them?

3. If the development is fully successful and removes some
natural limit to growth, what limit will the growing system
meet next? Will society prefer its pressures to the ones this
development is designed to remove?

Let us go on now to investigate nontechnical approaches for
dealing with growth in a finite world.

155

CHAPTER V

THE

STATE

GLOBAL
EQUILIBRIUM

Most persons think that a state in order
to be happy ought to be large; but
even it they are right, they have no idea
of what is a large and what a small

state To the size of states there is

a limit, as there is to other things, plants,
animals, implements; for none of these
retain their natural power when they are
too large or too small, but they either
wholly lose their nature, or are spoiled.

ARISTOTLE, 322 B.C.

We have seen that positive feedback
loops operating without any constraints generate exponential
growth. In the world system two positive feedback loops are
dominant now, producing exponential growth of population
and of industrial capital.

In any finite system there must be constraints that can act
to stop exponential growth. These constraints are negative
feedback loops. The negative loops become stronger and
stronger as growth approaches the ultimate limit, or carrying
capacity, of the system's environment. Finally the negative
loops balance or dominate the positive ones, and growth comes

156

THE STATE OF GLOBAL EQUILIBRIUM

to an end. In the world system the negative feedback loops
involve such processes as pollution of the environment, deple-
tion of nonrenewable resources, and famine.

The delays inherent in the action of these negative loops
tend to allow population and capital to overshoot their ulti-
mately sustainable levels. The period of overshoot is wasteful
of resources. It generally decreases the carrying capacity of the
environment as well, intensifying the eventual decline in
population and capital.

The growth-stopping pressures from negative feedback loops
are already being felt in many parts of human society. The
major societal responses to these pressures have been directed
at the negative feedback loops themselves. Technological solu-
tions, such as those discussed in chapter IV, have been devised
to weaken the loops or to disguise the pressures they generate
so that growth can continue. Such means may have some short-
term effect in relieving pressures caused by growth, but in the
long run they do nothing to prevent the overshoot and subse-
quent collapse of the system.

Another response to the problems created by growth would
be to weaken the positive feedback loops that are generating
the growth. Such a solution has almost never been acknowl-
edged as legitimate by any modern society, and it has certainly
never been effectively carried out. What kinds of policies would
such a solution involve? What sort of world would result?
There is almost no historical precedent for such an approach,
and thus there is no alternative but to discuss it in terms of
models— either mental models or formal, written models. How
will the world model behave if we include in it some policy
to control growth deliberately? Will such a policy change
generate a "better" behavior mode?

157

THE STATE OF GLOBAL EQUILIBRIUM

Whenever we use words such as "better" and begin choosing
among alternative model outputs, we, the experimenters, are
inserting our own values and preferences into the modeling
process. The values built into each causal relationship of the
model are the real, operational values of the world to the
degree that we can determine them. The values that cause us
to rank computer outputs as "better" or "worse" are the per-
sonal values of the modeler or his audience. We have already
asserted our own value system by rejecting the overshoot and
collapse mode as undesirable. Now that we are seeking a
"better" result, we must define our goal for the system as
clearly as possible. We are searching for a model output that
represents a world system that is:

1. sustainable without sudden and uncontrollable collapse; and

2. capable of satisfying the basic material requirements of all
of its people.

Now let us see what policies will bring about such behavior
in the world model.

DELIBERATE CONSTRAINTS ON GROWTH

You will recall that the positive feedback loop generating pop-
ulation growth involves the birth rate and all the socio-eco-
nomic factors that influence the birth rate. It is counteracted
by the negative loop of the death rate.

The overwhelming growth in world population caused by
the positive birth-rate loop is a recent phenomenon, a result of
mankind's very successful reduction of worldwide mortality.
The controlling negative feedback loop has been weakened,
allowing the positive loop to operate virtually without con-
straint. There are only two ways to restore the resulting im-

158

THE STATE OF GLOBAL EQUILIBRIUM

balance. Either the birth rate must be brought down to equal
the new, lower death rate, or the death rate must rise again.
All of the "natural" constraints to population growth operate
in the second way — they raise the death rate. Any society wish-
ing to avoid that result must take deliberate action to control
the positive feedback loop— to reduce the birth rate.

In a dynamic model it is a simple matter to counteract run-
away positive feedback loops. For the moment let us suspend
the requirement of political feasibility and use the model to
test the physical, if not the social, implications of limiting
population growth. We need only add to the model one more
causal loop, connecting the birth rate and the death rate. In
other words, we require that the number of babies born each
year be equal to the expected number of deaths in the popu-
lation that year. Thus the positive and negative feedback loops
are exactly balanced. As the death rate decreases, because of
better food and medical care, the birth rate will decrease

new link to stabilize population
by equating births and deaths

simultaneously. Such a requirement, which is as mathemati-
cally simple as it is socially complicated, is for our purposes
an experimental device, not necessarily a political recommen-

159

THE STATE OF GLOBAL EQUILIBRIUM

Figure 44 WORLD MODEL WITH STABILIZED POPULATION

In this computer run conditions in the model system are identical to those
in the standard run (figure 35), except that population Is held constant after
1975 by equating the birth rate with the death rate. The remaining un-
restricted positive feedback loop in the system, involving industrial capital,
continues to generate exponential growth of industrial output, food, and
services per capita Eventual depletion of nonrenewable resources brings
a sudden collapse of the industrial system.

dation* The result of inserting this policy into the model in
1975 is shown in figure 44.

• This suggestion for stabilizing population was originally proposed by
Kenneth E. Boulding in The Meaning of the 20th Century (New York:
Harper and Row, 1964).

160

THE STATE OF GLOBAL EQUILIBRIUM

In figure 44 the positive feedback loop of population growth
is effectively balanced, and population remains constant. At
first the birth and death rates are low. But there is still one
unchecked positive feedback loop operating in the model —
the one governing the growth of industrial capital. The gain
around that loop increases when population is stabilized,
resulting in a very rapid growth of income, food, and services
per capita. That growth is soon stopped, however, by depletion
of nonrenewable resources. The death rate then rises, but total
population does not decline because of our requirement that
birth rate equal death rate (clearly unrealistic here).

Apparently, if we want a stable system, it is not desirable
to let even one of the two critical positive feedback loops gen-
erate uncontrolled growth. Stabilizing population alone is not
sufficient to prevent overshoot and collapse; a similar run with
constant capital and rising population shows that stabilizing
capital alone is also not sufficient. What happens if we bring
both positive feedback loops under control simultaneously?
We can stabilize the capital stock in the model by requiring
that the investment rate equal the depreciation rate, with an
additional model link exactly analogous to the population-
stabilizing one.

industrial output

INDUSTRIAL

CAPITAL

(-)

depreciation

new link to
bv eauatina

161

THE STATE OF GLOBAL EQUILIBRIUM

Figure 45 WORLD MODEL WITH STABILIZED POPULATION
AND CAPITAL

Restriction of capital growth, by requiring that capital investment equal
depreciation, is added to the population stabilization policy of figure 44.
Now that exponential growth is halted, a temporary stable state is attained.
Levels of population and capital in this state are sufficiently high to deplete
resources rapidly, however, since no resource-conserving technologies
have been assumed. As the resource base declines, industrial output de-
creases. Although the capital base is maintained at the same level, effi-
ciency of capital goes down since more capital must be devoted to obtain-
ing resources than to producing usable output.

The result of stopping population growth in 1975 and in-
dustrial capital growth in 1985 with no other changes is shown
in figure 45. (Capital was allowed to grow until 1985 to raise
slightly the average material standard of living.) In this run

162

THE STATE OF GLOBAL EQUILIBRIUM

the severe overshoot and collapse of figure 44 are prevented.
Population and capital reach constant values at a relatively
high level of food, industrial output, and services per person.
Eventually, however, resource shortages reduce industrial out-
put and the temporarily stable state degenerates.

What model assumptions will give us a combination of a
decent living standard with somewhat greater stability than
that attained in figure 45 ? We can improve the model behavior
greatly by combining technological changes with value changes
that reduce the growth tendencies of the system. Different
combinations of such policies give us a series of computer out-
puts that represent a system with reasonably high values of
industrial output per capita and with long-term stability. One
example of such an output is shown in figure 46.

The policies that produced the behavior shown in figure 46
are:

1. Population is stabilized by setting the birth rate equal to
the death rate in 1975. Industrial capital is allowed to increase
naturally until 1990, after which it, too, is stabilized, by setting
the investment rate equal to the depreciation rate.

2. To avoid a nonrenewable resource shortage such as that
shown in figure 45, resource consumption per unit of industrial
output is reduced to one-fourth of its 1970 value. (This and the
following five policies are introduced in 1975.)

3. To further reduce resource depletion and pollution, the
economic preferences of society are shifted more toward ser-
vices such as education and health facilities and less toward
factory-produced material goods. (This change is made
through the relationship giving "indicated" or "desired"
services per capita as a function of rising income.)

163

THE STATE OF GLOBAL EQUILIBRIUM

4. Pollution generation per unit of industrial and agricultural
output is reduced to one-fourth of its 1970 value.

5. Since the above policies alone would result in a rather low
value of food per capita, some people would still be malnour-
ished if the traditional inequalities of distribution persist. To
avoid this situation, high value is placed on producing sufficient
food for all people. Capital is therefore diverted to food pro-
duction even if such an investment would be considered
"uneconomic." (This change is carried out through the "indi-
cated" food per capita relationship.)

6. This emphasis on highly capitalized agriculture, while neces-
sary to produce enough food, would lead to rapid soil erosion
and depletion of soil fertility, destroying long-term stability in
the agricultural sector. Therefore the use of agricultural capital
has been altered to make soil enrichment and preservation a
high priority. This policy implies, for example, use of capital
to compost urban organic wastes and return them to the land
(a practice that also reduces pollution).

7. The drains on industrial capital for higher services and food
production and for resource recycling and pollution control
under the above six conditions would lead to a low final level
of industrial capital stock. To counteract this effect, the average
lifetime of industrial capital is increased, implying better design
for durability and repair and less discarding because of obso-
lescence. This policy also tends to reduce resource depletion
and pollution.

In figure 46 the stable world population is only slightly
larger than the population today. There is more than twice
as much food per person as the average value in 1970, and
world average lifetime is nearly 70 years. The average indus-

THE STATE OF GLOBAL EQUILIBRIUM

Figure 46 STABILIZED WORLD MODEL I

mm vi ua"_ ' J iu j m uxmu i

Technological policies are added to the growth-regulating policies of the
previous run to produce an equilibrium state sustainable far Into the future.
Technological policies include resource recycling, pollution control de-
vices, increased lifetime of all forms of capital, and methods to restore
eroded and infertile soil. Value changes include increased emphasis on
food and services rather than on Industrial production. As in figure 45,
births are set equal to deaths and Industrial capital investment equal to
capital depreciation. Equilibrium value of industrial output per capita is
three times the 1970 world average.

trial output per capita is well above today's level, and services
per capita have tripled. Total average income per capita (indus-
trial output, food, and services combined) is about $1,800. This
value is about half the present average US income, equal to

165

THE STATE OF GLOBAL EQUILIBRIUM

the present average European income, and three times the
present average world income. Resources are still being gradu-
ally depleted, as they must be under any realistic assumption,
but the rate of depletion is so slow that there is time for tech-
nology and industry to adjust to changes in resource avail-
ability.

The numerical constants that characterize this model run
are not the only ones that would produce a stable system.
Other people or societies might resolve the various trade-offs
differently, putting more or less emphasis on services or food
or pollution or material income. This example is included
merely as an illustration of the levels of population and capital
that are physically maintainable on the earth, under the most
optimistic assumptions. The model cannot tell us how to attain
these levels. It can only indicate a set of mutually consistent
goals that are attainable.

Now let us go back at least in the general direction of the
real world and relax our most unrealistic assumptions — that
we can suddenly and absolutely stabilize population and capi-
tal. Suppose we retain the last six of the seven policy changes
that produced figure 46, but replace the first policy, beginning
in 1975, with the following:

1. The population has access to 100 percent effective birth
control.

2. The average desired family size is two children.

3. The economic system endeavors to maintain average indus-
trial output per capita at about the 1975 level. Excess industrial
capability is employed for producing consumption goods rather
than increasing the industrial capital investment rate above the
depreciation rate.

166

THE STATE OF GLOBAL EQUILIBRIUM

The model behavior that results from this change is shown
in figure 47. Now the delays in the system allow population
to grow much larger than it did in figure 46. As a consequence,
material goods, food, and services per capita remain lower than
in previous runs (but still higher than they are on a world
average today).

We do not suppose that any single one of the policies neces-
sary to attain system stability in the model can or should be
suddenly introduced in the world by 1975. A society choosing
stability as a goal certainly must approach that goal gradually.
It is important to realize, however, that the longer exponential
growth is allowed to continue, the fewer possibilities remain
for the final stable state. Figure 48 shows the result of waiting
until the year 2000 to institute the same policies that were
instituted in 1975 in figure 47.

In figure 48 both population and industrial output per capita
reach much higher values than in figure 47. As a result pol-
lution builds to a higher level and resources are severely de-
pleted, in spite of the resource-saving policies finally intro-
duced. In fact, during the 25-year delay (from 1975 to 2000)
in instituting the stabilizing policies, resource consumption is
about equal to the total 125-year consumption from 1975 to
2100 of figure 47.

Many people will think that the changes we have introduced
into the model to avoid the growth-and-collapse behavior mode
are not only impossible, but unpleasant, dangerous, even dis-
astrous in themselves. Such policies as reducing the birth rate
and diverting capital from production of material goods, by
whatever means they might be implemented, seem unnatural
and unimaginable, because they have not, in most people's
experience, been tried, or even seriously suggested. Indeed there

167

THE STATE OF GLOBAL EQUILIBRIUM

Figure 47 STABILIZED WORLD MODEL II

It the strict restrictions on growth of the previous run are removed, and
population and capital are regulated within the natural delays of the system,
the equilibrium level of population is higher and the level of Industrial
output per capita is lower than In figure 46. Here it is assumed that per-
fectly effective birth control and an average desired family size of two
children are achieved by 1975. The birth rate only slowly approaches the
death rate because of delays inherent in the age structure of the population.

would be little point even in discussing such fundamental
changes in the functioning of modern society if we felt that
the present pattern of unrestricted growth were sustainable
into the future. All the evidence available to us, however, sug-
gests that of the three alternatives— unrestricted growth, a self-

168

THE STATE OF GLOBAL EQUILIBRIUM

Figure 48 WORLD MODEL WITH STABILIZING POLICIES
INTRODUCED IN THE YEAR 2000

ft all the policies Instituted In 1975 In the previous figure ere delayed until
the year 2000, the equilibrium state Is no longer sustainable. Population
and Industrial capital reach levels high enough to create food and resource
shortages before the year 2100.

imposed limitation to growth, or a nature-imposed limitation
to growth— only the last two are actually possible.

Accepting the nature-imposed limits to growth requires no
more effort than letdng things take their course and waiting
to see what will happen. The most probable result of that deci-
sion, as we have tried to show here, will be an uncontrollable
decrease in population and capital. The real meaning of such a

169

THE STATE OF GLOBAL EQUILIBRIUM

collapse is difficult to imagine because it might take so many
different forms. It might occur at different times in different
parts of the world, or it might be worldwide. It could be
sudden or gradual. If the limit first reached were that of food
production, the nonindustrialized countries would suffer the
major population decrease. If the first limit were imposed by
exhaustion of nonrenewable resources, the industrialized coun-
tries would be most affected. It might be that the collapse
would leave the earth with its carrying capacity for animal
and plant life undiminished, or it might be that the carrying
capacity would be reduced or destroyed. Certainly whatever
fraction of the human population remained at the end of the
process would have very little left with which to build a new
society in any form we can now envision.

Achieving a self-imposed limitation to growth would require
much effort. It would involve learning to do many things in
new ways. It would tax the ingenuity, the flexibility, and the
self-discipline of the human race. Bringing a deliberate, con-
trolled end to growth is a tremendous challenge, not easily met.
Would the final result be worth the effort? What would
humanity gain by such a transition, and what would it lose?
Let us consider in more detail what a world of nongrowth
might be like.

THE EQUILIBRIUM STATE

We are by no means the first people in man's written history
to propose some sort of nongrowing state for human society.
A number of philosophers, economists, and biologists have
discussed such a state and called it by many different names,
with as many different meanings.*
We have, after much discussion, decided to call the state of

170

THE STATE OF GLOBAL EQUILIBRIUM

constant population and capital, shown in figures 46 and 47,
by the term "equilibrium." Equilibrium means a state of bal-
ance or equality between opposing forces. In the dynamic
terms of the world model, the opposing forces are those caus-
ing population and capital stock to increase (high desired
family size, low birth control effectiveness, high rate of capital
investment) and those causing population and capital stock
to decrease (lack of food, pollution, high rate of depreciation
or obsolescence). The word "capital" should be understood
to mean service, industrial, and agricultural capital combined.
Thus the most basic definition of the state of global equi-
librium is that population and capital are essentially stable,
with the forces tending to increase or decrease them in a care-
fully controlled balance.

There is much room for variation within that definition.
We have only specified that the stocks of capital and popula-
tion remain constant, but they might theoretically be constant

• See, for instance:
Plato, Laws, 350 B.C.
Aristotle, Politics, 322 B.C.

Thomas Robert Malthus, An Essay on the Principle of Population, 1798.
John Stuart Mill, Principles of Political Economy, 1857.
Harrison Brown, The Challenge of Man's Future (New York: Viking
Press, 1954).

Kenneth E. Boulding, "The Economics of the Coming Spaceship Earth,"

in Environmental Quality in a Growing Economy, ed. H. Jarrett

(Baltimore, Md.: Johns Hopkins Press, 1966).
E. J. Mishan, The Costs of Economic Growth (New York: Frederick

A. Praeger, 1967).
Herman E. Daly, "Toward a Stationary -State Economy," in The Patient

Earth, ed. J. Harte and Robert Socolow (New York: Holt, Rinehart,

and Winston, 1971).

171

THE STATE OF GLOBAL EQUILIBRIUM

at a high level or a low level — or one might be high and the
other low. A tank of water can be maintained at a given level
with a fast inflow and outflow of water or with a slow trickle
in and out. If the flow is fast, the average drop of water will
spend less time in the tank than if the flow is slow. Similarly,
a stable population of any size can be achieved with either
high, equal birth and death rates (short average lifetime) or
low, equal birth and death rates (long average lifetime). A
stock of capital can be maintained with high investment and
depreciation rates or low investment and depreciation rates.
Any combination of these possibilities would fit into our basic
definition of global equilibrium.

What criteria can be used to choose among the many options
available in the equilibrium state? The dynamic interactions
in the world system indicate that the first decision that must
be made concerns time. How long should the equilibrium state
exist? If society is only interested in a time span of 6 months
or a year, the world model indicates that almost any level of
population and capital could be maintained. If the time horizon
is extended to 20 or 50 years, the options are greatly reduced,
since the rates and levels must be adjusted to ensure that the
capital investment rate will not be limited by resource avail-
ability during that time span, or that the death rate will not
be uncontrollably influenced by pollution or food shortage.
The longer a society prefers to maintain the state of equilib-
rium, the lower the rates and levels must be.

At the limit, of course, no population or capital level can
be maintained forever, but that limit is very far away in time
if resources are managed wisely and if there is a sufficiently
long time horizon in planning. Let us take as a reasonable
time horizon the expected lifetime of a child born into the

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THE STATE OF GLOBAL EQUILIBRIUM

world tomorrow — 70 years if proper food and medical care
are supplied. Since most people spend a large part of their time
and energy raising children, they might choose as a minimum
goal that the society left to those children can be maintained
for the full span of the children's lives.

If society's time horizon is as long as 70 years, the permissible
population and capital levels may not be too different from
those existing today, as indicated by the equilibrium run in
figure 47 (which is, of course, only one of several possibilities).
The rates would be considerably different from those of today,
however. Any society would undoubtedly prefer that the death
rate be low rather than high, since a long, healthy life seems
to be a universal human desire. To maintain equilibrium with
long life expectancy, the birth rate then must also be low. It
would be best, too, if the capital investment and depreciation
rates were low, because the lower they are, the less resource
depletion and pollution there will be. Keeping depletion and
pollution to a minimum could either increase the maximum
size of the population and capital levels or increase the length
of time the equilibrium state could be maintained, depending
on which goal the society as a whole preferred.

By choosing a fairly long time horizon for its existence, and
a long average lifetime as a desirable goal, we have now arrived
at a minimum set of requirements for the state of global
equilibrium. They are:

1. The capital plant and the population are constant in size.
The birth rate equals the death rate and the capital investment
rate equals the depreciation rate.

2. All input and output rates — births, deaths, investment, and
depreciation—are \ept to a minimum.

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THE STATE OF GLOBAL EQUILIBRIUM

3. The levels of capital and population and the ratio of the two
are set in accordance with the values of the society. They may
be deliberately revised and slowly adjusted as the advance of
technology creates new options.

An equilibrium defined in this way does not mean stagna-
tion. Within the first two guidelines above, corporations could
expand or fail, local populations could increase or decrease,
income could become more or less evenly distributed. Tech-
nological advance would permit the services provided by a
constant stock of capital to increase slowly. Within the third
guideline, any country could change its average standard of
living by altering the balance between its population and its
capital. Furthermore, a society could adjust to changing inter-
nal or external factors by raising or lowering the population
or capital stocks, or both, slowly and in a controlled fashion,
with a predetermined goal in mind. The three points above
define a dynamic equilibrium, which need not and probably
would not "freeze" the world into the population-capital con-
figuration that happens to exist at the present time. The object
in accepting the above three statements is to create freedom
for society, not to impose a straitjacket.

What would life be like in such an equilibrium state ? Would
innovation be stifled? Would society be locked into the pat-
terns of inequality and injustice we see in the world today?
Discussion of these questions must proceed on the basis of
mental models, for there is no formal model of social condi-
tions in the equilibrium state. No one can predict what sort of
institutions mankind might develop under these new condi-
tions. There is, of course, no guarantee that the new society
would be much better or even much different from that which
exists today. It seems possible, however, that a society released

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THE STATE OF GLOBAL EQUILIBRIUM

from struggling with the many problems caused by growth
may have more energy and ingenuity available for solving
other problems. In fact, we believe, as we will illustrate below,
that the evolution of a society that favors innovation and
technological development, a society based on equality and
justice, is far more likely to evolve in a state of global equilib-
rium than it is in the state of growth we are experiencing today.

GROWTH IN THE EQUILIBRIUM STATE

In 1857 John Stuart Mill wrote:

It is scarcely necessary to remark that a stationary condition of capital
and population implies no stationary state of human improvement.
There would be as much scope as ever for all kinds of mental culture,
and moral and social progress; as much room for improving the Art of
Living and much more likelihood of its being improved. 4 *

Population and capital are the only quantities that need be
constant in the equilibrium state. Any human activity that
does not require a large flow of irreplaceable resources or pro-
duce severe environmental degradation might continue to grow
indefinitely. In particular, those pursuits that many people
would list as the most desirable and satisfying activities of
man — education, art, music, religion, basic scientific research,
athletics, and social interactions — could flourish.

All of the activities listed above depend very strongly on two
factors. First, they depend upon the availability of some sur-
plus production after the basic human needs of food and
shelter have been met. Second, they require leisure time. In
any equilibrium state the relative levels of capital and popula-
tion could be adjusted to assure that human material needs
are fulfilled at any desired level. Since the amount of material
production would be essentially fixed, every improvement in

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THE STATE OF GLOBAL EQUILIBRIUM

production methods could result in increased leisure for the
population — leisure that could be devoted to any activity that
is relatively nonconsuming and nonpolluting, such as those
listed above. Thus, this unhappy situation described by Ber-
trand Russell could be avoided:

Suppose that, at a given moment, a certain number of people are en-
gaged in the manufacture of pins. They make as many pins as the
world needs, working (say) eight hours a day. Someone makes an in-
vention by which the same number of men can make twice as many
pins as before. But the world does not need twice as many pins. Pins
are already so cheap that hardly any more will be bought at a lower
price. In a sensible world, everybody concerned in the manufacture of
pins would take to working four hours instead of eight, and everything
else would go on as before. But in the actual world this would be
thought demoralizing. The men still work eight hours, there are too
many pins, some employers go bankrupt, and half the men previously
concerned in making pins arc thrown out of work. There is, in the
end, just as much leisure as on the other plan, but half the men are
totally idle while half are still overworked. In this way it is insured
that the unavoidable leisure shall cause misery all around instead of
being a universal source of happiness. Can anything more insane be
imagined? 50

But would the technological improvements that permit the
production of pins or anything else more efficiently be forth-
coming in a world where all basic material needs are fulfilled
and additional production is not allowed? Does man have to
be pushed by hardship and the incentive of material growth
to devise better ways to do things ?

Historical evidence would indicate that very few key inven-
tions have been made by men who had to spend all their
energy overcoming the immediate pressures of survival. Atomic
energy was discovered in the laboratories of basic science by
individuals unaware of any threat of fossil fuel depletion. The

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THE STATE OF GLOBAL EQUILIBRIUM

first genetic experiments, which led a hundred years later to
high-yield agricultural crops, took place in the peace of a
European monastery. Pressing human need may have forced
the application of these basic discoveries to practical problems,
but only freedom from need produced the knowledge neces-
sary for the practical applications.

Technological advance would be both necessary and welcome
in the equilibrium state. A few obvious examples of the kinds
of practical discoveries that would enhance the workings of a
steady state society include:

• new methods of waste collection, to decrease pollution and
make discarded material available for recycling;

• more efficient techniques of recycling, to reduce rates of
resource depletion;

• better product design to increase product lifetime and pro-
mote easy repair, so that the capital depreciation rate would
be minimized;

• harnessing of incident solar energy, the most pollution-free
power source;

• methods of natural pest control, based on more complete
understanding of ecological interrelationships;

• medical advances that would decrease the death rate;

• contraceptive advances that would facilitate the equalization
of the birth rate with the decreasing death rate.

As for the incentive that would encourage men to produce
such technological advances, what better incentive could there
be than the knowledge that a new idea would be translated
into a visible improvement in the quality of life ? Historically
mankind's long record of new inventions has resulted in
crowding, deterioration of the environment, and greater social

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THE STATE OF GLOBAL EQUILIBRIUM

inequality because greater productivity has been absorbed by
population and capital growth. There is no reason why higher
productivity could not be translated into a higher standard
of living or more leisure or more pleasant surroundings for
everyone, if these goals replace growth as the primary value of
society.

EQUALITY IN THE EQUILIBRIUM STATE

One of the most commonly accepted myths in our present
society is the promise that a continuation of our present pat-
terns of growth will lead to human equality. We have demon-
strated in various parts of this book that present patterns of
population and capital growth are actually increasing the gap
between the rich and the poor on a worldwide basis, and that
the ultimate result of a continued attempt to grow according
to the present pattern will be a disastrous collapse.

The greatest possible impediment to more equal distribution
of the world's resources is population growth. It seems to be a
universal observation, regrettable but understandable, that, as
the number of people over whom a fixed resource must be
distributed increases, the equality of distribution decreases.
Equal sharing becomes social suicide if the average amount
available per person is not enough to maintain life. FAO
studies of food distribution have actually documented this
general observation.

Analysis of distribution curves shows that when the food supplies of
a group diminish, inequalities in intake are accentuated, while the num-
ber of undernourished families increases more than in proportion to the
deviation from the mean. Moreover, the food intake deficit grows with
the size of households so that large families, and their children in par-
ticular, are statistically the most likely to be underfed. 51

In a long-term equilibrium state, the relative levels of popula-

178

THE STATE OF GLOBAL EQUILIBRIUM

tion and capital, and their relationships to fixed constraints
such as land, fresh water, and mineral resources, would have
to be set so that there would be enough food and material pro-
duction to maintain everyone at (at least) a subsistence level.
One barrier to equal distribution would thus be removed. Fur-
thermore, the other effective barrier to equality — the promise
of growth — could no longer be maintained, as Dr. Herman E.
Daly has pointed out:

For several reasons the important issue of the stationary state will be
distribution, not production. The problem of relative shares can no
longer be avoided by appeals to growth. The argument that everyone
should be happy as long as his absolute share of wealth increases, re-
gardless of his relative share, will no longer be available. . . . The
stationary state would make fewer demands on our environmental re-
sources, but much greater demands on our moral resources. 62

There is, of course, no assurance that humanity's moral re-
sources would be sufficient to solve the problem of income dis-
tribution, even in an equilibrium state. However, there is even
less assurance that such social problems will be solved in the
present state of growth, which is straining both the moral and
the physical resources of the world's people.

The picture of the equilibrium state we have drawn here is
idealized, to be sure. It may be impossible to achieve in the
form described here, and it may not be the form most people
on earth would choose. The only purpose in describing it at
all is to emphasize that global equilibrium need not mean an
end to progress or human development. The possibilities with-
in an equilibrium state are almost endless.

An equilibrium state would not be free of pressures," since
no society can be free of pressures. Equilibrium would require
trading certain human freedoms, such as producing unlimited

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THE STATE OF GLOBAL EQUILIBRIUM

numbers of children or consuming uncontrolled amounts of
resources, for other freedoms, such as relief from pollution
and crowding and the threat of collapse of the world system.
It is possible that new freedoms might also arise — universal
and unlimited education, leisure for creativity and inventive-
ness, and, most important of all, the freedom from hunger and
poverty enjoyed by such a small fraction of the world's people
today.

THE TRANSITION FROM GROWTH TO GLOBAL EQUILIBRIUM

We can say very little at this point about the practical, day-by-
day steps that might be taken to reach a desirable, sustainable
state of global equilibrium. Neither the world model nor our
own thoughts have been developed in sufficient detail to under-
stand all the implications of the transition from growth to
equilibrium. Before any part of the world's society embarks
deliberately on such a transition, there must be much more dis-
cussion, more extensive analysis, and many new ideas con-
tributed by many different people. If we have stimulated each
reader of this book to begin pondering how such a transition
might be carried out, we have accomplished our immediate
goal.

Certainly much more information is needed to manage the
transition to global equilibrium. In the process of sifting the
world's data and incorporating it into an organized model, we
have become aware of the great need for more facts— lor num-
bers that are scientifically measurable but which have not yet
been measured. The most glaring deficiencies in present
knowledge occur in the pollution sector of the model. How
long does it take for any given pollutant to travel from its
point of release to its point of entrance into the human body ?
Does the time required for the processing of any pollutant into

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THE STATE OF GLOBAL EQUILIBRIUM

harmless form depend on the level of pollutant? Do several
different pollutants acting together have a synergistic effect on
human health? What are the long-term effects of low-level
dosages on humans and other organisms ? There is also a need
for more information about rates of soil erosion and land was-
tage under intensified modern agricultural practices.

From our own vantage point as systems analysts, of course,
we would recommend that the search for facts not be random
but be governed by a gready increased emphasis on establishing
system structure. The behavior of all complicated social sys-
tems is primarily determined by the web of physical, biological,
psychological, and economic relationships that binds together
any human population, its natural environment, and its eco-
nomic activities. Until the underlying structures of our socio-
economic systems are thoroughly analyzed, they cannot be
managed effectively, just as an automobile cannot be main-
tained in good running condition without a knowledge of how
its many parts influence each other. Studies of system structure
may reveal that the introduction into a system of some simple
stabilizing feedback mechanism will solve many difficulties.
There have been interesting suggestions along that line already
— for example, that the total costs of pollution and resource de-
pletion be included in the price of a product, or that every
user of river water be required to place his intake pipe down-
stream from his effluent pipe.

The final, most elusive, and most important information we
need deals with human values. As soon as a society recognizes
that it cannot maximize everything for everyone, it must begin
to make chdices. Should there be more people or more wealth,
more wilderness or more automobiles, more food for the poor
or more services for the rich? Establishing the societal an-

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THE STATE OF GLOBAL EQUILIBRIUM

swers to questions like these and translating those answers into
policy is the essence of the political process. Yet few people
in any society even realize that such choices are being made
every day, much less ask themselves what their own choices
would be. The equilibrium society will have to weigh the
trade-offs engendered by a finite earth not only with considera-
tion of present human values but also with consideration of
future generations. To do that, society will need better means
than exist today for clarifying the realistic alternatives available,
for establishing societal goals, and for achieving the alternatives
that are most consistent with those goals. But most important
of all, long-term goals must be specified and short-term goals
made consistent with them.

Although we underline the need for more study and discus-
sion of these difficult questions, we end on a note of urgency.
We hope that intensive study and debate will proceed simul-
taneously with an ongoing program of action. The details are
not yet specified, but the general direction for action is obvious.
Enough is known already to analyze many proposed policies in
terms of their tendencies to promote or to regulate growth.
Numerous nations have adapted or are considering programs
to stabilize their populations. Some localized areas are also
trying to reduce their rates of economic growth. 53 These ef-
forts are weak at the moment, but they could be strengthened
very quickly if the goal of equilibrium were recognized as de-
sirable and important by any sizable part of human society.

We have repeatedly emphasized the importance of the na-
tural delays in the population-capital system of the world.
These delays mean, for example, that if Mexico's birth rate
gradually declined from its present value to an exact replace-
ment value by the year 2000, the country's population would

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THE STATE OF GLOBAL EQUILIBRIUM

continue to grow until the year 2060. During that time the
population would grow from 50 million to 130 million. 54 If
the United States population had two children per family start-
ing now and if there were no net immigration, the population
would still continue to grow until the year 2037, and it would
increase from 200 million to 266 million. 55 If world population
as a whole reached a replacement-size family by the year 2000
(at which time the population would be 5.8 billion), the delays
caused by the age structure would result in a final leveling-off
of population at 8.2 billion 56 (assuming that the death rate
would not rise before then — an unlikely assumption, accord-
ing to our model results).

Taking no action to solve these problems is equivalent to
taking strong action. Every day of continued exponential
growth brings the world system closer to the ultimate limits
to that growth. A decision to do nothing is a decision to in-
crease the risk of collapse. We cannot say with certainty how
much longer mankind can postpone initiating deliberate con-
trol of his growth before he will have lost the chance for con-
trol. We suspect on the basis of present knowledge of the
physical constraints of the planet that the growth phase can-
not continue for another one hundred years. Again, because of
the delays in the system, if the global society waits until those
constraints are unmistakably apparent, it will have waited too
long.

If there is cause for deep concern, there is also cause for hope.
Deliberately limiting growth would be difficult, but not im-
possible. The way to proceed is clear, and the necessary steps,
although they are new ones for human society, are well within
human capabilities. Man possesses, for a small moment in his
history, the most powerful combination of knowledge, tools,

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THE STATE OF GLOBAL EQUILIBRIUM

and resources the world has ever known. He has all that is
physically necessary to create a totally new form of human
society — one that would be built to last for generations. The
two missing ingredients are a realistic, long-term goal that can
guide mankind to the equilibrium society and the human will
to achieve that goal. Without such a goal and a commitment
to it, short-term concerns will generate the exponential growth
that drives the world system toward the limits of the earth and
ultimate collapse. With that goal and that commitment, man-
kind would be ready now to begin a controlled, orderly transi-
tion from growth to global equilibrium.

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COMMENTARY

In inviting the MIT team to undertake this investigation, we
had two immediate objectives in mind. One was to gain
insights into the limits of our world system and the constraints
it puts on human numbers and activity. Nowadays, more than
ever before, man tends toward continual, often accelerated,
growth — of population, land occupancy, production, consump-
tion, waste, etc. — blindly assuming that his environment will
permit such expansion, that other groups will yield, or that
science and technology will remove the obstacles. We wanted
to explore the degree to which this attitude toward growth
is compatible with the dimensions of our finite planet and
with the fundamental needs of our emerging world society —
from the reduction of social and political tensions to improve-
ment in the quality of life for all.

A second objective was to help identify and study the domi-
nant elements, and their interactions, that influence the long-
term behavior of world systems. Such knowledge, we believe,
cannot be gathered by concentrating on national systems and
short-run analyses, as is the current practice. The project was
not intended as a piece of futurology. It was intended to be,
and is, an analysis of current trends, of their influence on each

COMMENTARY

other, and of their possible outcomes. Our goal was to pro-
vide warnings of potential world crisis if these trends are
allowed to continue, and thus offer an opportunity to make
changes in our political, economic, and social systems to ensure
that these crises do not take place.

The report has served these purposes well. It represents a
bold step toward a comprehensive and integrated analysis of
the world situation, an approach that will now require years
to refine, deepen, and extend. Nevertheless, this report is only
a first step. The limits to growth it examines are only the
known uppermost physical limits imposed by the finiteness
of the world system. In reality, these limits are further reduced
by political, social, and institutional constraints, by inequitable
distribution of population and resources, and by our inability
to manage very large intricate systems.

But the report serves further purposes. It advances tentative
suggestions for the future state of the world and opens new
perspectives for continual intellectual and practical endeavor
to shape that future.

We have presented the findings of this report at two inter-
national meetings. Both were held in the summer of 1971,
one in Moscow and the other in Rio de Janeiro. Although
there were many questions and criticisms raised, there was no
substantial disagreement with the perspectives described in this
report. A preliminary draft of the report was also submitted
to some forty individuals, most of them members of The Club
of Rome, for their comments. It may be of interest to mention
some of the main points of criticism:

1. Since models can accommodate only a limited number
of variables, the interactions studied are only partial. It was

186

COMMENTARY

pointed out that in a global model such as the one used in this
study the degree of aggregation is necessarily high as well.
Nevertheless, it was generally recognized that, with a simple
world model, it is possible to examine the effect of a change
in basic assumptions or to simulate the effect of a change in
policy to see how such changes influence the behavior of the
system over time. Similar experimentation in the real world
would be lengthy, costly, and in many cases impossible.

2. It was suggested that insufficient weight had been given
to the possibilities of scientific .nd technological advances in
solving certain problems, such as the development of fool-
proof contraceptive methods, the production of protein from
fossil fuels, the generation or harnessing of virtually limitless
energy (including pollution-free solar energy), and its subse-
quent use for synthesizing food from air and water and
for extracting minerals from rocks. It was agreed, however,
that such developments would probably come too late to avert
demographic or environmental disaster. In any case they
probably would only delay rather than avoid crisis, for the
problematique consists of issues that require more than tech-
nical solutions.

3. Others felt that the possibility of discovering stocks of raw
materials in areas as yet insufficiently explored was much
greater than the model assumed. But, again, such discoveries
would only postpone shortage rather than eliminate it. It must,
however, be recognized that extension of resource availability
by several decades might give man time to find remedies.

4. Some considered the model too "technocratic," observing
that it did not include critical social factors, such as the effects
of adoption of different value systems. The chairman of the

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COMMENTARY

Moscow meeting summed up this point when he said, "Man
is no mere biocybcrnetic device." This criticism is readily
admitted. The present model considers man only in his mate-
rial system because valid social elements simply could not be
devised and introduced in this first effort. Yet, despite the
model's material orientation, the conclusions of the study point
to the need for fundamental change in the values of society.

Overall, a majority of those who read this report concurred
with its position. Furthermore, it is clear that, if the argu-
ments submitted in the report (even after making allowance
for justifiable criticism) are considered valid in principle, their
significance can hardly be overestimated.

Many reviewers shared our belief that the essential signifi-
cance of the project lies in its global concept, for it is through
knowledge of wholes that we gain understanding of com-
ponents, and not vice versa. The report presents in straight-
forward form the alternatives confronting not one nation or
people but all nations and all peoples, thereby compelling a
reader to raise his sights to the dimensions of the world
problematique. A drawback of this approach is of course that
—given the heterogeneity of world society, national political
structures, and levels of development — the conclusions of the
study, although valid for our planet as a whole, do not apply
in detail to any particular country or region.

It is true that in practice events take place in the world
sporadically at points of stress — not generally or simultaneously
throughout the planet. So, even if the consequences anticipated
by the model were, through human inertia and political diffi-
culties, allowed to occur, they would no doubt appear first
in a series of local crises and disasters.

But it is probably no less true that these crises would have

COMMENTARY

repercussions worldwide and that many nations and people,
by taking hasty remedial action or retreating into isolationism
and attempting self-sufficiency, would but aggravate the con-
ditions operating in the system as a whole. The interdepen-
dence of the various components of the world system would
make such measures futile in the end. War, pestilence, a raw
materials starvation of industrial economies, or a generalized
economic decay would lead to contagious social disintegration.

Finally, the report was considered particularly valuable in
pointing out the exponential nature of human growth within
a closed system, a concept rarely mentioned or appreciated in
practical politics in spite of its immense implications for the
future of our finite planet. The MIT project gives a reasoned
and systematic explanation of trends of which people are but
dimly aware.

The pessimistic conclusions of the report have been and no
doubt will continue to be a matter for debate. Many will
believe that, in population growth, for instance, nature will
take remedial action, and birth rates will decline before catas-
trophe threatens. Others may simply feel that the trends
identified in the study arc beyond human control; these
people will wait for "something to turn up." Still others will
hope that minor corrections in present policies will lead to a
gradual and satisfactory readjustment and possibly to equilib-
rium. And a great many others are apt to put their trust in
technology, with its supposed cornucopia of cure-all solutions.

We welcome and encourage this debate. It is important,
in our opinion, to ascertain the true scale of the crisis con-
fronting mankind and the levels of severity it is likely to reach
during the next decades.

From the response to the draft report we distributed, we

COMMENTARY

believe this book will cause a growing number of people
throughout the world to ask themselves in earnest whether
the momentum of present growth may not overshoot the
carrying capacity of this planet — and to consider the chilling
alternatives such an overshoot implies for ourselves, our chil-
dren, and our grandchildren.

How do we, the sponsors of this project, evaluate the
report? We cannot speak definitively for all our colleagues in
The Club of Rome, for there are differences of interest,
emphasis, and judgment among them. But, despite the pre-
liminary nature of the report, the limits of some of its data,
and the inherent complexity of the world system it attempts
to describe, we are convinced of the importance of its main
conclusions. We believe that it contains a message of much
deeper significance than a mere comparison of dimensions, a
message relevant to all aspects of the present human predica-
ment.

Although we can here express only our preliminary views,
recognizing that they still require a great deal of reflection
and ordering, we are in agreement on the following points:

1. We are convinced that realization of the quantitative re-
straints of the world environment and of the tragic conse-
quences of an overshoot is essential to the initiation of new
forms of thinking that will lead to a fundamental revision
of human behavior and, by implication, of the entire fabric
of present-day society.

It is only now that, having begun to understand something
of the interactions between demographic growth and economic
growth, and having reached unprecedented levels in both,
man is forced to take account of the limited dimensions of

COMMENTARY

his planet and the ceilings to his presence and activity on it.
For the first time, it has become vital to inquire into the cost
of unrestricted material growth and to consider alternatives
to its continuation.

2. We are further convinced that demographic pressure in
the world has already attained such a high level, and is more-
over so unequally distributed, that this alone must compel
mankind to seek a state of equilibrium on our planet.

Underpopulated areas still exist; but, considering the world
as a whole, the critical point in population growth is approach-
ing, if it has not already been reached. There is of course no
unique optimum, long-term population level; rather, there are
a series of balances between population levels, social and
material standards, personal freedom, and other elements
making up the quality of life. Given the finite and diminishing
stock of nonrenewable resources and the finite space of our
globe, the principle must be generally accepted that growing
numbers of people will eventually imply a lower standard of
living — and a more complex problematique. On the other
hand, no fundamental human value would be endangered by a
leveling off of demographic growth.

3. We recognize that world equilibrium can become a reality
only if the lot of the so-called developing countries is sub-
stantially improved, both in absolute terms and relative to
the economically developed nations, and we affirm that this
improvement can be achieved only through a global strategy.

Short of a world effort, today's already explosive gaps and
inequalities will continue to grow larger. The outcome can
only be disaster, whether due to the selfishness of individual
countries that continue to act purely in their own interests,

COMMENTARY

or to a power struggle between the developing and developed
nations. The world system is simply not ample enough nor
generous enough to accommodate much longer such egocen-
tric and conflictive behavior by its inhabitants. The closer we
come to the material limits to the planet, the more difficult
this problem will be to tackle.

4. We affirm that the global issue of development is, however,
so closely interlinked with other global issues that an overall
strategy must be evolved to attack all major problems, includ-
ing in particular those of man's relationship with his environ-
ment.

With world population doubling time a little more than
30 years, and decreasing, society will be hard put to meet
the needs and expectations of so many more people in so
short a period. We are likely to try to satisfy these demands
by overexploiting our natural environment and further impair-
ing the life-supporting capacity of the earth. Hence, on both
sides of the man-environment equation, the situation will tend
to worsen dangerously. We cannot expect technological solu-
tions alone to get us out of this vicious circle. The strategy
for dealing with the two key issues of development and en-
vironment must be conceived as a joint one.

5. We recognize that the complex world problematique is to
a great extent composed of elements that cannot be expressed
in measurable terms. Nevertheless, we believe that the pre-
dominantly quantitative approach used in this report is an
indispensable tool for understanding the operation of the
problematique. And we hope that such knowledge can lead
to a mastery of its elements.

Although all major world issues are fundamentally linked,

COMMENTARY

no method has yet been discovered to tackle the whole effec-
tively. The approach we have adopted can be extremely useful
in reformulating our thinking about the entire human pre-
dicament. It permits us to define the balances that must exist
within human society, and between human society and its
habitat, and to perceive the consequences that may ensue when
such balances are disrupted.

6. We are unanimously convinced that rapid, radical redress-
ment of the present unbalanced and dangerously deteriorating
world situation is the primary task facing humanity.

Our present situation is so complex and is so much a reflec-
tion of man's multiple activities, however, that no combination
of purely technical, economic, or legal measures and devices
can bring substantial improvement. Entirely new approaches
are required to redirect society toward goals of equilibrium
rather than growth. Such a reorganization will involve a
supreme effort of understanding, imagination, and political
and moral resolve. We believe that the effort is feasible and
we hope that this publication will help to mobilize forces to
make it possible.

7. This supreme effort is a challenge for our generation. It
cannot be passed on to the next. The effort must be resolutely
undertaken without delay, and significant redirection must be
achieved during this decade.

Although the effort may initially focus on the implications
of growth, particularly of population growth, the totality of
the world problematique will soon have to be addressed. We
believe in fact that the need will quickly become evident for
social innovation to match technical change, for radical reform
of institutions and political processes at all levels, including

193

COMMENTARY

the highest, that of world polity. We are confident that our
generation will accept this challenge if we understand the
tragic consequences that inaction may bring.

8. We have no doubt that if mankind is to embark on a new
course, concerted international measures and joint long-term
planning will be necessary on a scale and scope without
precedent.

Such an effort calls for joint endeavor by all peoples, what-
ever their culture, economic system, or level of development.
But the major responsibility must rest with the more developed
nations, not because they have more vision or humanity, but
because, having propagated the growth syndrome, they are
still at the fountainhead of the progress that sustains it. As
greater insights into the condition and workings of the world
system are developed, these nations will come to realize that,
in a world that fundamentally needs stability, their high
plateaus of development can be justified or tolerated only if
they serve not as springboards to reach even higher, but as
staging areas from which to organize more equitable distri-
bution of wealth and income worldwide.

9. We unequivocally support the contention that a brake
imposed on world demographic and economic growth spirals
must not lead to a freezing of the status quo of economic
development of the world's nations.

If such a proposal were advanced by the rich nations, it
would be taken as a final act of neocolonialism. The achieve-
ment of a harmonious state of global economic, social, and
ecological equilibrium must be a joint venture based on joint
conviction, with benefits for all. The greatest leadership will
be demanded from the economically developed countries, for

194

COMMENTARY

the first step toward such a goal would be for them to encour-
age a deceleration in the growth of their own material output
while, at the same time, assisting the developing nations in
their efforts to advance their economies more rapidly.

10. We affirm finally that any deliberate attempt to reach a
rational and enduring state of equilibrium by planned mea-
sures, rather than by chance or catastrophe, must ultimately
be founded on a basic change of values and goals at individual,
national, and world levels.

This change is perhaps already in the air, however faintly.
But our tradition, education, current activities, and interests
will make the transformation embattled and slow. Only real
comprehension of the human condition at this turning point
in history can provide sufficient motivation for people to accept
the individual sacrifices and the changes in political and eco-
nomic power structures required to reach an equilibrium state.

The question remains of course whether the world situation
is in fact as serious as this book, and our comments, would
indicate. We firmly believe that the warnings this book con-
tains are amply justified, and that the aims and actions of our
present civilization can only aggravate the problems of tomor-
row. But we would be only too happy if our tentative assess-
ments should prove too gloomy.

In any event, our posture is one of very grave concern, but
not of despair. The report describes an alternative to unchecked
and disastrous growth and puts forward some thoughts on the
policy changes that could produce a stable equilibrium for
mankind. The report indicates that it may be within our
reach to provide reasonably large populations with a good
material life plus opportunities for limitless individual and

195

COMMENTARY

social development. We are in substantial agreement with
that view, although we are realistic enough not to be carried
away by purely scientific or ethical speculations.

The concept of a society in a steady state of economic and
ecological equilibrium may appear easy to grasp, although the
reality is so distant from our experience as to require a Coper-
nican revolution of the mind. Translating the idea into deed,
though, is a task filled with overwhelming difficulties and
complexities. We can talk seriously about where to start only
when the message of The Limits to Growth, and its sense of
extreme urgency, are accepted by a large body of scientific,
political, and popular opinion in many countries. The transi-
tion in any case is likely to be painful, and it will make extreme
demands on human ingenuity and determination. As we have
mentioned, only the conviction that there is no other avenue
to survival can liberate the moral, intellectual, and creative
forces required to initiate this unprecedented human under-
taking.

But we wish to underscore the challenge rather than the
difficulty of mapping out the road to a stable state society.
We believe that an unexpectedly large number of men and
women of all ages and conditions will readily respond to the
challenge and will be eager to discuss not if but how we can
create this new future.

The Club of Rome plans to support such activity in many
ways. The substantive research begun at MIT on world
dynamics will be continued both at MIT and through studies
conducted in Europe, Canada, Latin America, the Soviet
Union, and Japan. And, since intellectual enlightenment is
without effect if it is not also political, The Club of Rome also
will encourage the creation of a world forum where statesmen,

COMMENTARY

policy-makers, and scientists can discuss the dangers and hopes
for the future global system without the constraints of formal
intergovernmental negotiation.

The last thought we wish to offer is that man must explore
himself— his goals and values — as much as the world he seeks
to change. The dedication to both tasks must be unending.
The crux of the matter is not only whether the human species
will survive, but even more whether it can survive without
falling into a state of worthless existence.

The Executive Committee of The Club of Rome

ALEXANDER KING
SABURO OKITA
AURELIO PECCEI
EDUARD PESTEL
HUGO THIEMANN
CARROLL WILSON

197

APPENDIX: Related Studies

Papers related to the MIT System Dynamics Group- Club of
Rome Project on the Predicament of Mankind are listed below.
Most of these papers are available in one volume, Toward
Global Equilibrium: Collected Papers, Dennis L. Meadows,
editor. Published by Wright-Allen Press, Inc., 238 Main Street,
Cambridge, Massachusetts 02142.

Anderson, alison and Anderson, jay m. "System Simulation to
Test Environmental Policy III : The Flow of Mercury through
the Environment." Mimeographed. Cambridge, Mass.: Mas-
sachusetts Institute of Technology, 1971.

anderson, jay m. "System Simulation to Test Environmental
Policy II : The Eutrophication of Lakes." Mimeographed. Cam-
bridge, Mass.: Massachusetts Institute of Technology, 1971.

behrens, william w. in. "The Dynamics of Natural Resource
Utilization." Paper presented at the 1971 Summer Computer
Simulation Conference, July 1971, Boston, Massachusetts, spon-
sored by the Board of Simulation Conferences, Denver, Colo-
rado.

behrens, william w. hi and meadows, dennis l. "The De-
terminants of Long-Term Resource Availability." Paper pre-
sented at the annual meeting of the American Association for
the Advancement of Science, January 1971, Philadelphia,
Pennsylvania.

198

APPENDIX

choucri, nazli; laird, michael; and meadows, dennis l. "Re-
source Scarcity and Foreign Policy: A Simulation Model of
International Conflict." Paper presented at the annual meeting
of the American Association for the Advancement of Science,
January 1971, Philadelphia, Pennsylvania.

Forrester, jay w. "Counterintuitive Nature of Social Systems."
Technology Review 73 (1971) : 53.

Forrester, jay w. World Dynamics. Cambridge, Mass.:
Wright-Allen Press, 1971.

harbordt, steffen c. "Linking Socio-Political Factors to the
World Model." Mimeographed. Cambridge, Mass.: Massachu-
setts Institute of Technology, 1971.

meadows, donella h. "The Dynamics of Population Growth
in the Traditional Agricultural Village." Mimeographed. Cam-
bridge, Mass.: Massachusetts Institute of Technology, 1971.

meadows, donella h. "Testimony Before the Education Com-
mittee of the Massachusetts Great and General Court on Be-
half of the House Bill 3787." Republished as "Reckoning with
Recklessness," Ecology Today, January 1972, p. 11.

meadows, dennis l. The Dynamics of Commodity Production
Cycles. Cambridge, Mass.: Wright-Allen Press, 1970.

meadows, dennis l. "MIT-Club of Rome Project on the Pre-
dicament of Mankind." Mimeographed. Cambridge, Mass.:
Massachusetts Institute of Technology, 1971.

meadows, dennis l. "Some Requirements of a Successful En-
vironmental Program." Hearings of the Subcommittee on Air
and Water Pollution of the Senate Committee on Public
Works, Part I, May 3, 1971. Washington, DC: Government
Printing Office, 1971.

199

APPENDIX

milling, peter. "A Simple Analysis of Labor Displacement
and Absorption in a Two Sector Economy." Mimeographed.
Cambridge, Mass.: Massachusetts Institute of Technology, 1971.

naill, roger f. "The Discovery Life Cycle of a Finite Resource:
A Case Study of US Natural Gas." Mimeographed. Cambridge,
Mass.: Massachusetts Institute of Technology, 1971.

randers, j0rgen. "The Dynamics of Solid Waste Generation."
Mimeographed. Cambridge, Mass.: Massachusetts Institute of
Technology, 1971.

randers, J0RCEN and meadows, donella h. "The Carrying
Capacity of our Global Environment: A Look at the Ethical
Alternatives." In Western Man and Environmental Ethics, ed.
Ian Barbour. Reading, Mass.: Addison- Wesley, 1972.

randers, j0rgen and meadows, dennis l. "System Simulation
to Test Environmental Policy I: A Sample Study of DDT
Movement in the Environment." Mimeographed. Cambridge,
Mass.: Massachusetts Institute of Technology, 1971.

shantzis, Stephen b. and behrens, william w. hi. "Popula-
tion Control Mechanisms in a Primitive Agricultural Society."
Mimeographed. Cambridge, Mass.: Massachusetts Institute of
Technology, 1971.

200

NOTES

1. A. M. Carr-Saunders, World Population: Past Growth and Present
Trends (Oxford: Clarendon Press, 1936), p. 42.

2. US Agency for International Development, Population Program
Assistance (Washington, DC: Government Printing Office, 1970), p. 172.

3. World Population Data Sheet 1968 (Washington, DC: Population
Reference Bureau, 1968).

4. Lester R. Brown, Seeds of Change (New York: Praeger Publishers,
1970), p. 135.

5. President's Science Advisory Panel on the World Food Supply, The
World Food Problem (Washington, DC: Government Printing Office,
1967) 2:5.

6. President's Science Advisory Panel on the World Food Supply, The
World Food Problem, 2:423.

7. President's Science Advisory Panel on the World Food Supply, The
World Food Problem, 2:460-69.

8. UN Food and Agriculture Organization, Provisional Indicative
World Plan for Agricultural Development (Rome: UN Food and Agri-
culture Organization, 1970) 1:41.

9. Data from an Economic Research Service survey, reported by Rodney
J. Arkley in "Urbanization of Agricultural Land in California," mimeo-
graphed (Berkeley, Calif.: University of California, 1970).

NOTES

10. Paul R. Ehrlich and Anne H. Ehrlich, Population, Resources,
Environment (San Francisco, Calif.: W. H. Freeman and Company,
1970), p. 72.

11. Man's Impact on the Global Environment, Report of the Study of
Critical Environmental Problems (Cambridge, Mass.: MIT Press, 1970),
p. 118.

12. First Annual Report of the Council on Environmental Quality
(Washington, DC: Government Printing Office, 1970), p. 158.

13. US Bureau of Mines, Mineral Facts and Problems, 1970 (Wash-
ington, DC: Government Printing Office, 1970), p. 247.

14. Mercury data from US Bureau of Mines, Minerals Yearbook
(Washington, DC: Government Printing Office, 1967) 1(2):724 and
US Bureau of Mines, Commodity Data Summary (Washington, DC:
Government Printing Office, January 1971), p. 90. Lead data from
Metal Statistics (Somerset, NJ: American Metal Market Company,
1970), p. 215.

15. G. Evelyn Hutchinson, "The Biosphere," Scientific American,
September 1970, p. 53.

16. Chauncey Starr, "Energy and Power," Scientific American, Sep-
tember 1971, p. 42.

17. UN Department of Economic and Social Affairs, Statistical Year-
book^ 1969 (New York: United Nations, 1970), p. 40.

18. Bert Bolin, "The Carbon Cycle," Scientific American, September
1970, p. 131.

19. Inadvertent Climate Modification, Report of the Study of Man's
Impact on Climate (Cambridge, Mass.: MIT Press, 1971), p. 234.

20. John R. Clark, "Thermal Pollution and Aquatic Life," Scientific
American, March 1969, p. 18.

21. Inadvertent Climate Modification, pp. 151-54.

22. John P. Holdrcn, "Global Thermal Pollution," in Global Ecology,
ed. John P. Holdren and Paul R. Ehrlich (New York: Harcourt Brace
Jovanovich, 1971), p. 85.

23. Baltimore Gas and Electric Company, "Preliminary Safety Analysis

202

NOTES

Report," quoted in E. P. Ranford et al., "Statement of Concern,"
Environment, September 1969, p. 22.

24. R. A. Wallace, W. Fulkerson, W. D. Shults, and W. S. Lyons,
Mercury in the Environment (Oak Ridge, Tenn.: Oak Ridge Labora-
tory, 1971).

25. Man's Impact on the Global Environment, p. 131.

26. C. C. Patterson and J. D. Salvia, "Lead in the Modern Environ-
ment," Scientist and Citizen, April 1968, p. 66.

27. Second Annual Report of the Council on Environmental Quality
(Washington, DC: Government Printing Office, 1971), pp. 110-11.

28. Edward J. Kormandy, Concepts of Ecology (Englewood Cliffs,
NJ: Prentice-Hall, 1969), pp. 95-97.

29. Second Annual Report of the Council on Environmental Quality,
p. 105.

30. Calculated from average GNP per capita by means of relationships
shown in H. B. Chenery and L. Taylor, "Development Patterns:
Among Countries and Over Time," Review of Economics and Statistics
50 (1969): 391.

31. Calculated from data on metal and energy consumption in UN
Department of Economic and Social Affairs, Statistical Yearbook 1969.

32. J. J. Spengler, "Values and Fertility Analysis," Demography 3
(1966): 109.

33. Lester B. Lave and Eugene P. Seskin, "Air Pollution and Human
Health," Science 169 (1970): 723.

34. Second Annual Report of the Council on Environmental Quality,
pp. 105-6.

35. Frank W. Notestein, "Zero Population Growth: What Is It?"
Family Planning Perspectives 2 (June 1970): 20.

36. Donald J. Bogue, Principles of Demography (New York: John
Wiley and Sons, 1969), p. 828.

37. R. Buckminster Fuller, Comprehensive Design Strategy, World
Resources Inventory, Phase II (Carbondale, 111.: University of Illinois,
1967), p. 48.

203

NOTES

38. Thomas S. Lovering, "Mineral Resources from the Land," in
Committee on Resources and Man, Resources and Man (San Francisco,
Calif.: W. H. Freeman and Company, 1969), p. 122-23.

39. Second Annual Report of the Council on Environmental Quality,
p. 118.

40. Garrett Hardin, "The Cybernetics of Competition: A Biologist's
View of Society," Perspectives in Biology and Medicine 7 (Autumn
1963): 58, reprinted in Paul Shepard and Daniel McKinley, eds., The
Subversive Science (Boston: Houghton Mifflin, 1969), p. 275.

41. S. R. Sen, Modernizing Indian Agriculture vol. 1, Expert Commit-
tee on Assessment and Evaluation (New Delhi: Ministry of Food,
Agriculture, Community Development, and Cooperatives, 1969).

42. For an excellent summary of this problem see Robert d'A. Shaw,
fobs and Agricultural Development, (Washington, DC: Overseas De-
velopment Council, 1970).

43. Richard Critchfield, "It's a Revolution All Right," Alicia Patterson
Fund paper (New York: Alicia Patterson Fund, 1971).

44. Robert d'A. Shaw, fobs and Agricultural Development, p. 44.

45. Lester R. Brown, Seeds of Change, p. 112.

46. US Bureau of the Census, /970 Census of Population and Housing,
General Demographic Trends of Metropolitan Areas, 1060-yo (Wash-
ington, DC: Government Printing Office, 1971).

47. Garrett Hardin, "The Tragedy of the Commons," Science 162
(1968): 1243.

48. UN Food and Agriculture Organization, The State of Food and
Agriculture (Rome: UN Food and Agriculture Organization, 1970),
p. 6.

49. John Stuart Mill, Principles of Political Economy, in The Col-
lected Wor\s of John Stuart Mill, ed. V. W. Bladen and J. M. Robson
(Toronto: University of Toronto Press, 1965), p. 754.

50. Bertrand Russell, In Praise of Idleness and Other Essays (London:
Allen and Unwin, 1935), pp. 16-17.

204

NOTES

51. UN Food and Agriculture Organization, Provisional Indicative
World Plan for Agricultural Development 2: 490.

52. Herman E. Daly, "Toward a Stationary-State Economy," in The
Patient Earth, ed. John Harte and Robert Socolow (New York: Holt,
Rinehart, and Winston, 1971), pp. 236-37.

53. See, for example, "Fellow Americans Keep Out!" Forbes, June 15,
1971, p. 22, and The Ecologist, January 1972.

54. J. Bourgeois-Pichat and Si-Ahmed Taleb, "Un taux d'acroissetrient
nul pour les- pays en voie de developpement en l'an 2000: Reve ou
realite?" Population 25 (September/October 1970): 957.

55. Commission on Population Growth and the American Future, An
Interim Report to the President and the Congress (Washington, DC:
Government Printing Office, 1971).

56. Bernard Berelson, The Population Council Annual Report, igjo
(New York: The Population Council, 1970), p. 19.

205

"... likely to be one of the most important documents ot
our age." ANTHONY LEWIS, in the New York Times

The message of this book is urgent and
sobering: The earth's interlocking re-
sources — the global system of nature in
which we all live — probably cannot sup-
port present rates of economic and popu-
lation growth much beyond the year 2100,
if that long, even with advanced tech-
nology.

In the summer of 1970, an international
team of researchers at the Massachusetts
Institute of Technology began a study of
the implications of continued worldwide
growth. They examined the five basic
factors that determine and, in their inter-
actions, ultimately limit growth on this
planet — population increase, agricultural
production, nonrenewable resource deple-
tion, industrial output, and pollution gener-
ation. The MIT team fed data on these five
factors into a global computer model and
then tested the behavior of the model under
several sets of assumptions to determine
alternative patterns for mankind's future.
THE LIMITS TO GROWTH is the nontech-
nical report of their findings.

The book contains a message of hope, as
well: Man can create a society in which he
can live indefinitely on earth if he imposes
limits on himself and his production of
material goods to achieve a state of global
equilibrium with population and production
in carefully selected balance.

"The most important business on earth,
quite literally, is the business of planetary
planning. This book is a pioneering effort in
that direction. It has something ot value to
say to anyone who understands the pre-
carious realities ot the human habitat."
NORMAN COUSINS, editor and author

"If this book doesn't blow everybody's

mind who can read without moving his lips.

then the earth is kaput."

ROBERT C. TOWNSEND, author of Up the

Organization and former president and

chief executive officer of Avis Rent A Car

Corporation

"This book raises lite-and-death questions
that confront mankind as it strives tor
achievement ot a prosperous and equit-
able society."

VERNON E. JORDAN, JR.. executive
director, National Urban League

"The Meadows and the MIT team have
done a great service in constructing a
preliminary model of the world in which all
the assumptions and parameters are
explicit and thus open to criticism and
modification. Those who object to the char-
acteristics ot the model are challenged to
help improve it; those who dislike the char-
acteristics ot the system it simulates might
consider working for changes in the real
world."

PAUL EHRLICH, professor of biology at
Stanford University

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